22 



KNOWLEDGE. 



[February 1, 1892. 



i. Spores 

 ii. Gemmffi . 



iii. Protouemn 



always produces the Moss plant, the vegetable growth with 

 its stem and its leaves. To the production of this all else 

 is subordinate ; it is the one thing needful. 



On the other hand, the one thing which Nature seems 

 desirous to avoid is the sexual reproduction by the concur- 

 rence of the two organs of the archegones and the antherids. 

 Tills is found only in the one mode of growth ; every other 

 kind of reproduction by gemma, by protonema, by bud, all 

 of course leave out the whole sporophytic generation. 



In the following table, which is far from exhaustive, I 

 have endeavoured to exhibit some of the modes of repro- 

 duction, dividing them into those cases in which it takes 

 place with protonema and those cases in which it takes 

 place without. 



Table C. — Modes of Eeproduction. 



A. — With Protonema. 

 in capsiile. 



rLeptodontium gemmasciins. 

 on end of leaf } Orthotrichum j)(i!(IIa7i(hniii. 



L^irhnmia Uartmalii, 



on midrib Tortulo papilloso. 



in axils of leaves ... Briixim. 



in balls AuJacomnion. 



in cups Ti(in)))iis. 



from zhizoids iv''i"T'1- 



from aerial rbizoids... Dtcranum wndulatum. 

 from terminal lejives. OTicopJiorits glaucit:^. 

 from base of leaf ... Fitnaria hygrometricn. 



from midrib Oyfhotrichum LycUi. 



from margin Buxbavmia ajihylla, 



from stems ., JXcranum undulatuw. 



from calyptra COTicmifi-ium jiiIioTitim. 



B. — WitJiout Protonema. 



iv. Leaf-Buds ... on rbizoids Grimmiapnlv!nata. 



v. Leaf-Buds ... on .aerial rbizoids ... Dicranum imdxilatiim. 



vi. Bulbs on stem Sryvm aiinotinum. 



Tii. Young Plants, at ends of brancbes ... Spiiagmim cuspidatxm. 

 Tiu. Leaf. Branches, becominsr detached ( Cnnoiiii-fi-ium .jultoimm. 



'" (.tinciiaotns aqiiattciis. 

 is. Booting of main ) „ . 



axis j Mninvi vnaiitatum, 



Weismann's Theory. — The consideration of this table, and 

 of the facts which are epitomized in it, is not without its 

 interest in reference to Prof. Weismann's theory of the 

 division of the cells and the plasma of organisms into two 

 kinds : the germ cells and germ plasma endowed with a 

 natural immortality, and the somatic cells and somatic 

 plasma possessing no such endowment. That the Mosses 

 are a difficulty in the acceptance of the theory as a universal 

 truth, the professor liimself admits. The evidence of the 

 Mosses seems to amount at least to this : that in this whole 

 group, the highest in this line of development, where the 

 oophytic generation produces the principal plant, and where 

 there are highly specialized organs fur the production of 

 spores or germ cells — that in this whole group either there 

 is no efl'ectual separation between the two kinds of plasma, 

 or that the germ plasma is so mdely diffused amongst the 

 somatic plasma that every portion of the plant is capable 

 of reproducing the entire organism. 



Compariso7i with Zooloyical Embn/olof/i/. — The table will 

 further offer us some points of comparison with animal 

 embryology. 



In that branch of physiology, one of the most remarkable 

 facts is what has been called recapitulation, i.e., the sum- 

 mary in the life of the individual of the life of the race, so 

 that the development of the individual tells the development 

 of the race — e.i/., the gills of the tadpole tell us of the 

 descent of the Batrachians from gill-breathing animals. 



So here we cannot doubt that the protonema of the 

 Moss tells us of the descent of the whole group of Mosses 

 from the AlgfE. 



Another remarkable fact in animal embryology is the 



co-existence in exceptional cases of the mature and the 



immature form : so the asolotl retains both gills and lungs 



throughout its life. In like manner some Mosses retain 



' their algoid protonema throughout life. 



The Phascum or Clay Moss is a conspicuous instance of 



It is a Moss of 



ciispi- 



FlG. 17. — Phascum 

 datum. <7, capsule; r,rliizoid9; 

 j[). persistent protonema. After 

 Scliimper. 



this curious fact : it is depicted in Fig. 17. 

 a not very high organization. 

 The leaves grow close to the " 



ground and the stem is very 

 short. In like manner the 

 sporangium (a) is almost 

 sessile, and is seen almost 

 enshrouded in the leaves, 

 true rootlets or rbizoids (c) 

 attach the plant to the ground, 

 and the protonema (ji) from 

 which the plant has arisen 

 survives and remains at- 

 tached to it during the whole 

 life of the plant. This 

 protonema often exists in 

 great quantity in the clay 

 banks or fields where the 

 Phascum dwells, and forms a sort of tangled mat. 



Again, in zoological embryology, an attempt is often 

 found, to use the language of Prof. Milnes Marshall, " to 

 escape from the necessity of recapitulating, and to sub- 

 stitute for the ancestral process a more direct method." 



In like manner we have already seen to how great an 

 extent Nature has adopted the system of short-circuiting 

 in the reproduction of the Mosses ; for in every mode of 

 reproduction, except that through sporogone and spore, a 

 shorter circuit is travelled. We have seen how in every 

 case Nature seems to leave out the sexual reproduction if 

 she can help it, and directs her whole attention to the 

 production of the vegetative organism — the Moss plant Ln 

 the popular sense — which she never omits. 



Another point of comparison arises, but this time it is one 

 of contrast between the embryology of the two kingdoms. 



In animals, to again quote Prof. Milnes Marshall, " re- 

 capitulation is not seen in all forms of development, but 

 only in sexual development, or at least only in development 

 from the egg. In the several forms of asexual development 

 of which budding is the most frequent and the most 

 familiar, there is no repetition of ancestral phases, neither 

 is there in cases of regeneration of lost parts." 



In Mosses, on the contrary, the table last given shows 

 that in most of the modes of reproduction the ancestral 

 form, the algoid protonema, is retained and reproduced, 

 whereas in the growth from a sexual cell, i.e. in the 

 sporogone, the ancestral form entirely disappears. 



Un/a7n:ation. — I now propose to describe somewhat 

 more in detail certain parts of the structure of a Moss. 



The stem of Mosses is, as we have already seen, very 

 variable in size. Sometimes, as in the Phascum (Fig. 17), 

 the whole plant is almost sessile ; in other cases, as in 

 the Polytrichum (Fig. 2), it attains to a very considerable 

 length. In some Mosses inhabiting water, the length of 

 the plant reaches to feet. In our flowering plants the 

 stem is supportei by the presence of fibro-vascular 

 bundles, i.e., fibres arranged in combination with tubes 

 along which fluids can and do pass. But with the ex- 

 ception of one family, the stem of the Mosses, like all the 

 other parts of the plant, is constituted of cells alone, and 

 consequentl}' the circulation of fluid in them appears to 

 result entirely from the passage of fluid through the walls 

 of the cells. Hence their close dependence on the 

 presence of moisture ; hence in dry weather they fade and 

 droop, and with the return of moisture assume their 

 wonted appearance. 



The exception to which I have referred exists in the 

 family of the Polytrichacefe, of which the genus Poly- 

 trichum is the foremost (Figs. 2 and 3). In that kind of 

 Moss the stem of the plant and the stalks that support the 



