A TRICHUM UXDULA TL MA 99 



significant and interesting than the leaf bundle of the 

 midrib. It is the simplest form of a structure that 

 plays a most important part in higher plants the 

 framework of wood and bark which enables them to rise 

 above the surface of the earth and display their tissues 

 to the wind and sun under conditions most favor- 

 able for growth. The bundles of Atrichum which are 

 as highly developed as in any of the mosses, resemble 

 those of higher plants more in their position and 

 function than in structure. 8 Their place in the leaf 

 and their manner of forming leaf-traces in the stem are 

 like those of higher plants. The cells for strength are 

 the dorsal and ventral, being the same except in posi- 

 tion, and the cells inclosed by these transport the sap. 



Passing to the sexual reproduction, we notice that 

 the organs concerned are much like those of Marchantia. 

 The differences requiring consideration lie in the modes 

 of displaying and protecting the organs. Instead of 

 sinking the male organs in a flattened receptacle, they 

 are placed in the axils of protecting leaves diverted to 

 that use, and instead of bringing the female organs 

 under the protecting roof of the receptacle they are 

 sheltered from rain and other excessive moisture by 

 the overlapping of the perichaetial leaves. 



An item of historical interest in this connection is 

 that it was in the mosses that the sexual organs of 

 cryptogams were first demonstrated by Hedwig 4 in 

 1783, but it was not till the publication of Suminski's 

 researches on the ferns, 5 as late as 1848, that their 



3 A very full illustrated account of the histology of the stem and leaves 

 of mosses is given in Pringsheim's Jahrb. f. wis. Bot., vi. 



4 Theoria Generationis, p. 138. 



5 Zur Entw. der Farrnkrauter. 



