Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries Part 58

In the fields a young Ranunculus in profusion, Veronica agrestis, Euphorbia, Festuca annua?

Kochia spinosa, and a curious Mathioloid are among the few wild plants to be found about Pushut.

It would be a curious circ.u.mstance if all indusiate ferns were to be found reducible to a _marginal production_ of the reproductive apparatus. I will bear this in mind, as certain forms of Pteris or its affinities lead me to suspect that in these tribes the indusium may be a long way from the margin, and yet be, quoad origin, marginal; this section ill.u.s.trates my meaning.

[Fern sections: m444.jpg]

The transition to this might reasonably be suspected. The philosophy of ferns is most ill understood, the higher points connected with them have been quite neglected, and botanists in this as in other departments of the science have been contented to confer names on certain external forms, without sufficient regard to structure.

To-day I commenced examining Adiantum, with the view of determining if possible the nature of its reproductive organs, and the mode in which they are impregnated, if they are impregnated at all.

As I had long been aware that the fructification of each frond is a thing to be determined at a very early period, and that if not determined then, it is never likely to be determined afterwards, my attention was directed more strongly, if possible, than it would have been otherwise, to examining the subject at the earliest possible stage of its development.

The first piece examined gave me the idea that I had trouve le noeud de l'affaire; the second made me doubt this; the subsequent ones went far to disprove it.

I was immediately struck with the resemblance of those organs, called ramenta, to what are fairly a.s.sumed to be the male bodies, in certain other families of the same grand division; and I at once came to the conclusion, that the barren fronds, were barren, because almost dest.i.tute of these ramenta; and that as these ramenta were confined to the base of the stalk, that is, to the part below its first ramification, an obvious necessity existed for the peculiar nature of the vernation.

Further examination of the thing, especially of the base of the stipes and the adjoining part of the rhizoma, threw me back almost into my original difficulties. I find that the rhizoma is entirely covered with ramenta, which are brown, much detached at the base, and obviously represent a low form of leaf, i.e. in appearance, perhaps partly in function, but not in structure. Among these, mature ramenta at the punctas of prolongation, which appear to be very irregular, are concealed, others much smaller, and much narrower, (which bear as obvious a resemblance, or even more so to the male organs of certain other orders,) than the ramenta on the stipes. These are never entirely brown, the end cell alone is coloured, but though occasionally tinged with brown, they are filled with some fluid (even this is not so at first,) but do not appear to open. I believe that subsequently all become highly tinged with brown, but what increase of growth they subsequently undergo, I know not. The terminal cell is always solitary, very often attached to the one next it, which is generally single, obliquely placed, occasionally looking like the dimidiate calyptra capping a young seta.

The number of cells forming the base, or dilated part varies, but is always small in proportion to the larger ramenta, or protecting scales: these last have a single terminal cell, which in fact must be the same in every really cellular growth _sooner or later_, the last degree of formative power being the production of a single cell.

At a subsequent period, still an early one, the terminal cell is fuscous- brown, and this colour then extends to the next in various degrees, but if it reaches the basilar ones at all, it does so at late periods. The base of the terminal cell, and parts of the parietes of the next and next, present a coagulated appearance, precisely as in certain mosses.

No such thing as a petiolate leaf occurs in acrogens, all are attached by a broad base? Of acrogenous leaves, those only are leaves whose attachment is at right angles with the stem; the rest are divisions of a frond. Thus far with the ramenta. The divisions of the frond, are, I find, not gyrate, but rather cochleariform involate. The future reproductiveness is settled at a very early period, and is distinguishable under the microscope by a sort of _margination_ of the frondlets. In the earliest stage I have looked at, the margin is greenish, striated by narrow cells, and pa.s.ses into the body of the leaf gradually; the greater development is perhaps central; even now the bulk of the cells of the leaflet have green granules, and are opaque from air.

The vessels are marked out, or at least their future course, and along them the opacity from air does not exist, so that the veins appear depressed.

The next stage presented a greater development of an isolation of the margin, but no other change. The next presented an isolation of the margin, which remains almost white, the other part being green, but more so because of a thickening as it were along the base of the marginal part, and an evident deposit of grumous matter, from which, under every circ.u.mstance new tissue seems always to be developed. Pressure causes its discharge, its contents were unappreciated by my poor instruments; after this the leaflets revert to the appearance of the second stage.

Here I ceased for the day, having I think ascertained that ferns are endorhizal, and that the primary divisions of the roots hence have sheaths, which adhere to the apex of the root itself.--What a strange union of roots, that of monocotyledons in the main divisions, and of pure acrogens in the minor!!

I cannot help thinking that the secret is hidden in these ramenta, which, as is known, are so universal as obviously to have higher functions than those of mere covering scales. The appearance of those I have described as existing about the points of growth, are exactly the same as the processes mixed with the anthers of mosses, and of which the anthers are nothing but more developed growths; this would point out, as indeed appears to me otherwise evident, (especially from consideration of the theca, and its want of style,) that ferns are lower organised as s.e.xual beings than mosses and Hepaticae. I know nothing of Lycopodineae, more than they are the highest of all acrogens; and are not to be included in the same category with ferns.

The objection to the ramenta being anthers, will be the closed nature (_apparently_) of the terminal cell, and although the anthers of mosses do burst, and most especially those of Hepaticae, yet the argument is not conclusive--inasmuch as _boyaux_, to which they are a.n.a.logous _do not_ _open_?

These ramenta explain fully the nature of those confervoid organs found in some Neckerae, and perhaps in other mosses, and it becomes paramount to prove whether these Neckerae have also the usual anthers, or if they are confined to these, in which case a presumptive proof will thus be afforded of their functions: if they have both forms, they will nevertheless const.i.tute an a.n.a.logous pa.s.sage between the two orders: if they have only _these_, such Neckerae will form, as indeed they do, a very distinct genus.

The nature of the barren fronds requires distinct a.n.a.lysis. Are they barren from mere deficiency in supplies, such as may result from many circ.u.mstances; or are the antheriform ramenta deficient? They are barren from defective growth. I am aware how readily objection may be taken to these views, some will say these young ramenta are nothing but young scales as the older ones evidently are scales; but this amounts to nothing, because we may expect simplicity in the s.e.xual organs of this division, and it will be only a proof of the uniformity of nature in making so great a difference in a function depend on, or be a.s.sociated with so small a one in form. My view I think explains their uniformly brown colour--a.n.a.logous to Brown's sphacelation in mutatis mutandis.

Others will say how absurd the idea is, when you cannot show the place to which the impregnating influence is to be applied. But the consideration of mosses does away with this objection partly, and that of Anthoceros, entirely; because in mosses, the _ovule_, or pre-existing cell, ready to receive the male influence becomes an empty cell, terminating the seta; and the sporula become developed at its opposite end, the first growth appearing to be quite unconnected with that of the future reproductive organs: and in Anthoceros there is no fixed punctum ready for the application of the male organs, but these have to form a communication with the lower, or inferior cellular tissue of the frond, before even the growth of seta can commence.

Besides a case in point exists in Visc.u.m, or Loranthus, in which no point is ready prepared for the reception of the male influence; showing how universal the law is, that in no one point or place is there an absolute want of gradation.

As in mosses the influence of the male _disregarding the ovule_, is thrown into the development of the seta, and then of the theca at the apex of this; there can be no conclusive reason why in ferns the same influence should be thrown into the development of the frond, and then into that of the theca.

While Anthoceros proves that in these orders the male influence may exert its effects upon any point.

As there is no styliform production in Anthoceros, so there is none in ferns. If the ramenta be anthers, they will not be dubious ones, because as they remain fixed, people cannot say, that possibly they are also reproductive bodies, which by the bye is no objection at all, after instances of anthers bearing _ovules_ instead of pollen!

Why the peculiar distribution of the male influence (on which we determine our genera,) takes place, is another question, and one that cannot be fairly asked?

Why it is confined to the under surface perhaps can, it being a law that in all cases it is the under surface of the leaf, or its modification, from which new growths originate, and as nature has closed indusia, how could the under surface be interior if this rule were not regularly adhered to?

That the indusium is a _special_ organ, i.e. not an eruption of the cuticle, I am sure; hence it is essential to examine extensively both indusiate and other forms, the precise extension of their veins, etc. at an early period to ascertain if their most diversified situations cannot be reduced to some one type.

_Query_. Is the gyrate vernation of any ferns comparable to the form of certain sh.e.l.ls, to which (at least Mollusca) ferns are supposed to be a.n.a.logous.

_Memo_. To ascertain the most peculiar, and most universal points of Mollusca and Pseudo cotyledonea, it is in this way that we may hope to extend our views. Some there are indeed who, while the whole course of their studies has been to neglect structure, deny the applicability of presumptive evidence in favour of doctrines, the subjects of which are barely susceptible of direct proof. Thus Greville and Arnott, angrily ask, what do persons mean by saying that mosses have pistilla, etc.? they protest against such community of application in the use of terms. Many more deny s.e.xuality because it has not been proved. Considering the invisible nature of the fluid of the anthers of mosses, etc. how do they expect that we are to demonstrate its application to the pistil, and the subsequent steps? As well might they doubt the necessity of the application of the boyau to an ovule, (or the existence of the boyau itself,) because the derivation of the embryo cannot be proved.

One word more; in all cases the appearance of the reproductive body after impregnation, is of late date; that date becomes later as we descend the scale. The embryonary sac of Phaenogams does not always exist at the time of application of the boyau, and the appearance of the embryo is always posterior to this.

Again, ferns are superior to mosses in this, that in many cases the male influence is exerted directly on the parts that become the thecae, which is not the case in mosses.

_18th_.--Continued examining ferns, and to-day completes my knowledge of the ramenta of three different genera.

In the first which is Cryptogamma, the resemblance of the young ramenta to the anthers of Jungermannia is evident enough, they are capital, and the head is at one period filled with granular matter: so are the cells throughout, to a greater or less extent. They are to be seen in all stages of development on the pinnae of a very young frond, those near its base having perhaps effected their purpose, while those at the apex of the pinna, or the prolonging part of pinnula, may be formed of only one cell. It is curious that the terminal cell does not become spherical for some time: in its earlier stages it is cylindrical like the rest.

The appearances of the old ones are, if possible, more markedly in favour of my hypothesis; there is the same aggregation of grumous _congealed_ matter about the ends of each cell, the same curious communication between these ma.s.ses which hide the septa from view, evincing a greater or less tendency to a.s.sume the peculiar fuscesent or fus...o...b..own appearance. I observed in two instances what appeared to me decided irregular openings in the terminal cell, from one of which grumous filaments projected; these appeared to communicate with the ma.s.s in the terminal cell, which like that in all the others, is congealed; but it a.s.sumes a different and very undefined form.

People may object and say, why were not more met with _opened_? This is no objection, because it is obvious that a spherical body may be opened in part of its surface, and yet unless this portion happens to be on the _edge_ as it were of the sphere, it may escape detection with a microscope of poor penetration.

In this the ramenta are confined, or nearly so, to the under surface of the fronds. Most occupy that which is called the costa. In this the first change as in Adiantum is in the definition of the margin. But this point I have not paid much attention to, as with my present means here, it would be absurd to attempt _proving_ how the fecundation takes place; all that I can attempt is, to ascertain from structure and a.n.a.logy, the male nature of these curious bodies.

_See_ Plate _B_ for the various sketches. {450}

The next genus examined, is perhaps the instance in which these ramenta have the strongest resemblance to ordinary simple hairs, both in their young, when they represent succulent, tinged, grumous molecular-containing hairs, and in the old, when they represent long, flattened, coriaceous hairs, still there is abundant evidence to prove that, however different these bodies are in appearance from those of Cryptogamma, that they undergo the same changes, excepting perhaps as to dehiscence. We have a tendency to fuscous colouring, a tendency to the aggregation of congealed matter about the septae, precisely the places where it is to be expected. The same appearance of a ca.n.a.l of communication, the same irregular _constriction_ of certain cells; in this too the first change in the pinnae, or its component lobes, is the definition of the margin. In this genus the under surface of the frond is covered with these _hairy-form_ bodies (which have been figured over and over again in Hooker and Greville's ferns): on the upper face, a few exist, but incomparably less developed.

From the examination of this genus alone, I do not think the idea I have been so diffuse upon, would have struck me.

To-morrow I examine Ceterach, a.s.sured that the scales of its under face are reducible to the same type. In a matter of such interest and importance as this, many will, and with reason, dislike so important an a.s.sumption on such inconclusive evidence. But with our present means, it appears to me probable that no evidence to demonstration can be looked for, and for this reason, that the contents of these peculiar cells are so subtile as to escape definition even while in their cells, (or under the most favourable circ.u.mstance for a concentration of attention.) How much more so will this be the case, when we attempt to examine the steps of the application of the fecundatory matter, applied over a surface without any prominent points, and probably opaque.

When direct evidence is not to be had, we are justified in using presumptive evidence. As in human law, so in the laws of nature, presumptive evidence to a practised eye carries with it conviction. We have no direct evidence how the embryo is formed, yet no one doubts but that it is brought about by the agency of the boyau, which is a cell containing grumous molecular matter. However different a boyau may seem to many, yet when viewed in conjunction with Cycadeae, the graduation to the present case becomes natural, and even the resemblance may be perfect, because in Cycas the grains of pollen get into the nucleus bodily, although they would still seem to throw out short tails.

Wonderful is the simplicity of nature! The male organ in its essence, consists of a single cell containing molecular matter.

The female in its essence consists of a single cell, likewise containing similar matter. The influence of the male is exerted, and so another cell is formed in the female cell, and this either becomes the embryo, or gives origin to another cell, and so on, until the terminal one becomes the embryo.

I believe from examination of the most developed scaly ramenta, that these have at an earlier period been fecundating organs, the same peculiarities are to be detected towards their ends, where in fact they retain their original structure, the dilated base being a subsequent development.

In reference to this, the examination of young ferns on their arrival at the age of p.u.b.erty is indispensable. A curious question arises, what is the frond of a fern? Is it a ma.s.s of foliaceous growth containing certain lines of reproductive matter, or is it a distinct development from the axis, in which the reproductive organs are situated? Is it, or is it not, subservient to reproduction? Here again extensive examination is necessary.

If it is altogether subordinate to reproduction, we may expect the occurrence of far more simply const.i.tuted ferns than we are yet acquainted with. In fact we may expect a form reduced to an axis, a few ramenta, a frondose dilatation, and one punctum of reproductive organs.

With respect to duration, each frond is a.n.a.logous to a single seta of a moss, it has definite limits, and is unlike the fronds of certain Hepaticae, which are capable of compound growth; or if this is the case in ferns, as it is in viviparous ferns, the new formation becomes separated from the frond, as a Phaenogamous gemma does. This is a question of importance, as perhaps it may prove that all the foliaceous forms, except Lycopodium, Equisetum, and Chara, are frondose; the dorsal situation is in favour of this a.s.sumption, since in all the genuine frondose forms, the reproductive organs of both kinds originate immediately from the under surface, although they may protrude through the upper.

I here ask, is there not _prima facie_ evidence that these organs have peculiar functions; a peculiar form, attended with peculiar changes, must have peculiar functions; and will any one show me in any single instance, like circ.u.mstances to the like extent, in any of those organs called hairs? By the bye, ferns themselves may prove that however like these are to certain forms of hair, yet that their functions are different, because the glandular hairs of ferns do not undergo the same alterations, and are evidently nothing but hairs, probably secretory.

_19th_.--In Ceterach the same thing occurs precisely, with this difference, that the _capita_ of the ramenta are highly developed; and still more, that the terminations of each pinnula of the young frond, are mere scales without a terminal _head_.

So that almost all the scales of the under surface of the lobes of the mature frond, are mere scales. The peculiar ramenta are to be looked for along the insertion of each pinna, and along the rachis, in which all have the peculiar structure.

At the time that these scales are commencing their development, the peculiar ones are at the age of mature perfection, so far as function goes. No one can look at a young pinnula at this epoch and observe the evident capitation of each ramentum, the inflexion of its apex, so that the head is brought into contact with the frond, without suspecting that they have the same relation of _cause_ to the appearance subsequently of the thecae or capsules. It is curious that the colour of the scales is the same as that of the ramenta, in which the colour is developed from above _downwards_, a peculiarity as it appears to me.