53 c ACROGENS. 



" In the Mosses the vegetative life is exclusively committed to the first, the pro- 

 duction of fruit to the second generation. Only the leafy stem possesses roots ; the 

 spore-producing generation draws its sustenance from the foregoing. The fruit is 

 usually of shorter duration than the leaf-bearing plant. In the Filicoids the opposite 

 condition obtains. It is true the prothallia send out capillary rootlets ; those of the 

 PolypodiaoeSB and Equisetacese under all circumstances, those of the Rhizocarpese and 

 Selaginellse frequently. But the prothallium has a much briefer existence than the 

 frondescent plant; which in most cases must vegetate for several years before it comes 

 to bear fruit. Yet the contrast is not so strong as it appears to be at first sight. The 

 seemingly unlimited duration of the leaf-bearing Moss-plant depends upon constant 

 renovation. Phenomena essentially similar occur in proliferous prothallia of the Poly- 

 podiaccso and Equisetacese. The structure of the lowest (Anthoceros, Pellia) is less 

 complex, and the duration of the fruit-bearing shoots is little longer than that of the 

 fruit itself. On the other hand, the ramification of the prothallium of the Equise- 

 tacese is exceedingly complicated; its duration is even equal to that of a single 

 shoot. 



" It is a circumstance worthy of notice, that in the second generation of Mosses, as 

 of the Filicoids, destined to produce spores, more complex thickenings of the cell- 

 walls regularly occur (teeth of the peristome of Mosses, wall of capsule and elaters of 

 Liverworts, vessels of Filicoids, &c), while in the first generation, springing from the 

 spores, such structures are found only rarely and as exceptions. 



" The manner in which the second generation arises from the first, varies much 

 more in the Filicoids than in the Mosses. The Polypodiacese and Equisetacese are 

 hermaphrodite ; the Rhizocarpese and Selaginellse monoecious. All the Filicoids 

 agree in the fact that the first axis of their embryo possesses but a very limited 

 longitudinal development ; that it is an axis of the second rank which breaks through 

 the prothallium and becomes the main axis ; further, in the end of the axis of the 

 first rank never becoming elongated in the direction opposite to the summit. All 

 Filicoids are devoid of a tap-root, and possess only adventitious roots. 



" In more than one respect does the course of development of the embryo of the 

 Conifers stand intermediately between those of the higher Cryptogams and the 

 Phanerogams. Like the primary parent-cell of the spores of the Rhizocarpese and 

 Selaginellse, the einbryo-sac is an axile cell of the shoot, which in the former is 

 converted into a sporangium, in the latter into an ovule. In the Conifers the embryo- 

 sac also very early becomes detached from the cellular tissue surrounding it. 

 The filling-up of the embryo-sac with the albumen may be compared with the origin 

 of the prothallium in the Rhizocarpese and Selaginellse. The structure of the 

 ' corpuscula' bears the most striking resemblance to that of the archegonia of Salvinia, 

 still more to that of the Selaginellse. If we leave out of view the different nature of 

 the impregnation, in the Rhizocarpese and Selaginellse by free-swimming spermatic 

 filaments, in the Conifers© by a pollen-tube (which perhaps developes spermatic 

 filaments in its interior), the metamorphosis of the embryonal vesicle into the 

 primary parent-cell of the new plant in the Conifers and Filicoids is solely 

 distinguished, by the latter possessing only a single embryonal vesicle which com- 

 pletely fills the cavity of the central cell of the archegonium, while the former 

 exhibits very numerous embryonal vesicles swimming in it, of which only one pressed 

 into the lower end of the ' corpusculum' becomes impregnated. The embryo-sac of 

 the Conifers may be regarded as a spore which remains enclosed in its sporangium ; 

 the prothallium which it forms never comes to light. The fertilising matter must 

 make a way for itself through the tissue of the sporangium, to reach the archegonia of 

 this prothallium." 



I confess that I am by no means satisfied with some of these opinions. The 

 adoption of Steenstrup'a theory of alternate generations seems to arise too much from 

 « pnort considerations, and the statements regarding the impregnating action of the 

 jpiral filaments in Ferns appears to be wholly hypothetical. 



Let us take for illustration Hofmeister's account of the development of the organs 

 of Lypocods (A nnalcs des Sciences, ser. 3, xviii. 183.) It is only in Selaginella helvetica, 

 says this author, that he has been able to make out what happens in the micro- 

 spores (powdery matter) after they are sown. In the beginning of March he sowed 

 them in earth ana sand kept constantly moist. Five months afterwards, he found 

 is each microspore, almost without exception, a great quantity of small spherical 

 vcs,cl,.s, whose diameter was scarcely equal to ^ of a line, and which did not quite 

 nu the cavrfg in which they were lodged. When these microspores were carefully 

 pressed, the vesicles were easily squeezed out, and there appeared in some of them 

 a very tine spiral thread, or spermatozoid, which, when liberated, stirred with a 

 gentle motion. This is no doubt a remarkable fact ; but it stops short of the proof 



