390 



MOSSES AND FERNS 



CHAP. 



embryo, while others creep into special cavities which are found 

 in all the leaves except the cotyledon, and here develop into a 

 colony. 



The first branch is formed after the plant has developed 



B 



in 



Fig. 200. — Azolla JiUcidoides (Lam.). Nearly median section of the young sporophyte after it has 

 broken through the prothallium, x 100 ; B, an older plant with the macrospore {sp) still attached ; 

 7«, massulse attached to the base of the macrospore ; r. the primarj' root, X 40. 



about eight leaves, but whether its position is constant was not 

 determined. 



The Mature Sporophyte 



Strasburger ^ has investigated very completely the tissues 

 of the mature sporophyte of Azolla, and Pringsheim - has done 

 the same in Salvinia, so that these points are very satisfactorily 

 understood. 



The growing point of the stem in Azolla (Fig. 201, A) is 

 curved upward and backward, in Salvinia (Fig. 203, A) it is 

 nearly horizontal. In both genera there is a two-sided apical 

 cell from which segments arise right and left. Each segment 

 divides into a dorsal and ventral cell, and a transverse section 

 just back of the apex shows four cells arranged like quadrants 

 of a circle. In Azolla the dorsal cells develop the leaves, the 

 ventral ones the branches and roots. Each semi-segment is 



^ Strasburger (6). 



- Pringsheim (i). 



