Feb. 15, 1877J 



NATURE 



331 



quently happens that the young prothallium gets arrested 

 in its development without reaching the stage in which 

 archegonia are produced, such prothalHawill beexclusively 

 male by arrest of development. It can hardly be doubted 

 that in an analogous manner male flowers have arisen in 

 diclinous flowering plants. In Osimmda amongst ferns 

 the complete dioecious condition is reached. There can, 

 in fact, be no doubt that ferns are habitually cross-fer- 

 tilised, and there is also good reason to believe that they 

 are even hybridised. It is further noteworthy that whilst in 

 Osimmda there is an agamic reproduction of the prothallial 

 generation, in a few rare cases, as pointed out first by Dr. 

 Farlow, the process of gamogenesis is wholly in abey- 

 ance and the prothallium gives rise to the spore-bearing 

 stage agamogenetically. One might remark here that 

 the probable absence of true gamogenesis amongst the 

 larger fungi might be compared with this abnormal occur- 

 rence in ferns. But another explanation suggests itself. 

 Amongst the Myxoinycctes the continuous masses of pro- 

 toplasm which constitute the plant in its active stale, 

 segregate into spores which eventually set free zoospores. 

 These swim about to again coalesce into a plasmodium, 

 Sachs has suggested that this coalescence is of a sexual 

 character, and in fact a kind of multi-conjugation ; and no 

 doubt the zoospores, in their motile condition, will un- 

 dergo a certain amount — inconceivably minute it may be 

 — of differentiation, due to slight differences in exposure 

 to external conditions such as heat and light, and thus the 

 end of a more regular sexual process may be attained. In 

 the higher fungi there is nothing exactly comparable with 

 this unless we compare with the fusion of zoospores in the 

 Myxomycetes the habitual inosculation and intergrafcing 

 of the mycelial threads, the result of which must be to 

 bring about an intermixture of somewhat differentiated 

 protoplasm. 



Perhaps, therefore, on a review of Mr. Darwin's remarks 

 on the subject of hermaphroditism (pp. 409, 410), one may 

 demur to his conclusion that the monoecious condition " is 

 probably the first step towards hermaphroditism." It seems 

 not improbable that precisely the converse maybe the more 

 true. Mr. Darwin thinks " that as plants became more 

 highly developed and affixed to the ground they would be 

 compelled to become anemophilous in order to intercross. 

 Therefore all plants which have not since been greatly 

 modified would tend still to be both diclinous and ane- 

 mophilous." But it does not appear that it is intended to 

 limit this statement to flowering plants ; yet it would 

 certainly require some modification amongst Pterido- 

 phyta for example. As we have seen, ferns, at any rate, 

 are not diclinous, nor are they anemophilous, yet they 

 escape all the evil results possibly attending the herma- 

 phrodite condition. The fact is that as long as plants 

 possess motile antherozoids, and their sexual processes 

 take place not in mid-air, but on damp soil, there is no 

 need for the intervention of agencies like the wind or 

 insects to bring about cross-fertilisation. The natural loco- 

 motive powers possessed by the antherozoids are sufficient 

 to secure that. The difficulty began when the very limited 

 mobility of the pollen tube was substituted for the amazing 

 activity of the antherozoid. And it will throw a great 

 deal of light on the question as to whether the primordial 

 flower was diclinous or not if one considers the manner in 

 which it probably originated. 



In the first place, it must be remembered that the pro- 

 cesses which take place in a " flower" are, in a vascular 

 cryptogam, spread over two distinct generations. The 

 drama which once had two acts is now compressed into 

 one. Bearing this in mind, we shall find little difficulty in 

 seeing in the sporangiiferous cone or spike of SelcK^inella 

 the homologue of the flower. For, like that, it is com- 

 posed essentially of an axis bearing modified lateral 

 appendages, some of which, in this case the upper ones, 

 produce male structures — microspores — and the lower — fe- 

 male ones — macrospores. These bodies fall to the ground, 

 and those from adjacent plants are more or less com- 

 mingled by the wind before sexual interaction begins to 

 take place. Now, comparing a flower, we find that it also 

 consists of an axis with modified lateral appendages, and 

 if we call the embryo-sac a macrospore and the pollen- 

 grain a microspore, as we are thoroughly justified in 

 doing, then the only important difference between a " ^S"^- 

 /(7^/«,?//rt:-fructification " and a " flower " is that the 

 position on the axis of microspore- and macrospore-pro- 

 ducing structures is inverted. 



How, then, do we proceed from one to the other .? 

 Simply by prolonging the period during which micro- 

 spores and macrospores remain attached to the parent 

 plant. Instead of fertilisation being effected on soil 

 moist enough to allow the antherozoids to move, sup- 

 pose it take place on the parent plant in a comparatively 

 dry atmosphere. Antherozoids are no longer set free by 

 the microspore, which simply puts out processes (of which 

 those from the microspore of Salvinia — forming the very 

 rudimentary male prothallia — are a kind of foreshadowing) 

 towards the female organs developed from the macrospore. 

 And there is precedent, for example, amongst the Sapro- 

 legniea:, for such a reversion to a mode of fertilisation 

 resembling conjugation (which fertilisation by a pollen 

 tube really is) from a phase of motile antherozoids. 



There is a probability, then, that a flower originated by 

 the retention of macrospores (more especially) within the 

 structures of some plant-form not distantly related to 

 Selagmella— such a flower would be extremely incon- 

 spicuous, destitute of colour — these modifications being 

 only subsequently acquired — and, what is more important, 

 hermaphrodite. Diclinous flowers would arise simply by 

 the arrest of development of either the male or female 

 organs, and this arrest would be only one of the several 

 modes by which nature determines the cross-fertilisation 

 which we now know to be beneficial, and therefore 

 likely to be secured by the self-adjusting process of 

 natural selection. This view, by which flowers are re- 

 garded as originally hermaphrodite, instead of, as Mr. 

 Darwin suggests, monoecious, further supplies a very 

 simple explanation of the otherwise almost inexplicable 

 nature of cleistogene flowers. These being inconspicuous 

 and self-fertilising — are probably survivals of the original 

 type. 



I am happy to be able to support what I have urged by 

 the following passages from Mr. Bentham's presidential 

 address to the Linnean Society in 1873. Criticising Stras- 

 burger's views as to the pedigree of phanerogams (which 

 derived them from the diclinous Conifers), he remarks 

 that if we accept them, 



" We must suppose that races, after having once 

 secured the advantages of a total separation of the two 



