14 



BOTANY 



with its segmentation into stem and leaves, is frequently termed a 

 CORMUS, and the plants themselves Cormophytes. To the Cormo- 

 phytes belong all plants from the Mosses upwards. 



Transition from the Thallus to the Cormus. — The lowest division 

 of the Bryophytes, the Liverworts {Hepaticae), although in many cases 



Fig. 10. — Ricciaftuitans. 

 (Nat. size.) 



Fig. 11. — Blasia pusilki. s, Sporogonium ; 

 r, rhizoids. (x2.) 



possessing thalloid bodies without any segmentation into members, 

 contain also forms with the same differentiation into stem and leaves 



as the higher plants. As between these 

 two extremes there may be found transi- 

 tional forms, this class of plants, accord- 

 ingly, affords valuable assistance in the 

 phylogenetic study of the development of 

 higher plants. A few examples will best 

 illustrate these stages of differentiation 

 exhibited by the Hepaticae. The bifur- 

 cately branching thallus of Riccia fluitans 

 (Fig. 10) is flat and ribbon-like, and in 

 its general appearance resembles the 

 thallus of the previously mentioned brown 

 Alga, Dictyota dichotoma (Fig. 8). A more 

 advanced development is shown by Blasia 

 pusilla (Fig. 11), which has incisions in 

 the sides of its ribbon-like body. The 

 lobes thus formed by the lateral incisions, 

 as is shown by comparison with other 

 more highly differentiated Hepaticae, and 

 also by the study of their development, 

 are properly to be regarded as rudimental leaves. Finally, in Plagio- 

 chila asplenioides (Fig. 12), with alternating ovate leaves and elongated 

 fibrous stems, the segmentation into stem and leaf is complete. 



The Cormus. — With the segmentation into stem and leaf, the 



Fig. 12. — Plagiochila asplenioides. 

 a, Sporogonium. (Nat. size.) 



