BRYOPHYTES. 



49 



As will be suggested with regard to the same 

 phenomena in the higher plants, the lamellar out- 

 growths and the union of the surfaces of two distinct 

 leaves may represent one and the same phenomenon 

 exhibiting different degrees of development, or under 

 different forms. 



This may or may not be the case. It is not likely to 

 be so if these abnormal outgrowths from the lower 

 surface are of the same nature as the curious lamellar 

 enations from the midrib which occur normally in 



r - 



J(J. 



Fig. 10. — Atrichum undulatum. Base of seta enveloped by sheathing 

 leaf ; paraphyses (p,p) at base. (After Potier de la Varde.) 



Pterygoneurd, Grossidium, and Barbula on the upper 

 surface of the leaf. In Polytrichiim they are merely 

 trichomes springing from the epidermal cells. Schimper 

 also mentions the normal occurrence of median lamellae 

 in Pottia subsessiMs and Fissidens addantoides. 



In contrast to all the above-cited instances of increase 

 of the leaf-surface is that of the leaves of young plants 

 of the moss Amblystegium glaticum, which were reduced 

 to their midribs. 



Boot and, Protonema. — In view of their great simi- 

 larity, these two organs will be considered together. 

 The "root" of the sexual generation is the rhizoid, 

 and this organ would seem to be really homologous 



vol. i. 4 



