404 



MOSSES AND FERNS 



CHAP. 



that Azolla, does, but from two of the corners long wing-like 

 appendages hang down, and the whole prothallium is saddle- 

 shaped. The side joining the two wings is the front, and the 

 primary archegonium occupies the highest point, as in Azolla, 



t B. C. 



FIG. 236. Azolla filiculoides. Development of the embryo, X35Q. A, B, C, Young 

 embryos in median longitudinal section; D, two horizontal sections of a young 

 embryo; E, three transverse sections of a somewhat older one; x, x' , initial cells 

 of the cotyledon; F, two longitudinal sections of an advanced embryo; G, hori- 

 zontal section of an older one, with the rudiments of the second and third leaves; 

 b, b, basal wall of the embryo; st, stem; L 1 , cotyledon; r, root; h, hairs; x, apical 

 cell of the stem; L 2 , L 3 , second and third leaves. 



and the two secondary ones form a line with it parallel to the 

 forward edge, which develops a meristem and other archegonia 

 in rows parallel to the first ones, in case these fail to be fer- 

 tilised. 



In Azolla the prothallium has but little power of independ- 



