RECENT WORK ON MOSSES AND FERNS. 359 



established, as applied to the details of development of the 

 Archegoniatse ; and subsequent work, even the best of it, 

 has done little more than fill in the details of the design 

 which he sketched in its broad outlines. But while Hof- 

 meister, after the manner of a pre-Darwinian writer, pro- 

 ceeded on lines of pure comparison of iorm and structure, 

 at the present time the tendency is towards a more physio- 

 logical view. The attempt is being made to distinguish 

 those characters which are most liable to change under 

 varied external conditions from those which are more 

 constant, and so to arrive at a more reasonable understand- 

 ing of the true relations of organisms one to another as 

 regards descent. What is readily mutable now under 

 varied conditions has probably been mutable in the past 

 also, and will be a less safe character for comparison than 

 those features which persistently retain their form while the 

 conditions vary. We shall see subsequently how important 

 a bearing these matters have on opinion as to the relation- 

 ships of the Archegoniatae. 



The point which emerged most prominently from the 

 writings of Hofmeister was the phenomenon ol ''alterna- 

 tions of oenerations " in the Archeg-oniatai. A feature of 

 so wide a bearing as this may, with some certainty, be taken 

 as the morphological expression of some far-reaching causes. 

 However open to the accusation of guess-work, suggestions 

 have been made as to the origin of this wonderful pheno- 

 menon, and the hypothetical story may be told in brief as 

 follows : — 



The origin of the great green-coloured series of plants, 

 comprising virtually the whole of our land flora, was pro- 

 bably from aquatic forms resembling the green-coloured 

 Algae of the present day. Among the simplest of these we 

 find that external conditions may directly determine the 

 succession of events ; it has been shown in the case of 

 Vauckeria 1 that the operator has it in his power to induce, by 



1 " Zur. Phys. d. Fortpfl. v. Vaucheria sessilis," G. Klebs. Verh. 

 d. Naturf. Ges. in Basel, 1895. Also G. Klebs, " Ueber d. Vermehrung 

 V. Hydrodictyon utriculatum ". Flora, 1890. 



