XI 



LEPTOSPORANGIAT^ HETEROSPOREM 



417 



massulae look as if composed of cells. The tapetal nuclei are 

 confined to the outside of the massulae, and can be detected al- 

 most up to the time they are fully developed. Finally, upon 

 the outside of the massulse are formed the curious anchor-like 

 "glochidia" (Fig. 234, gl) , whose flattened form is due to their 

 formation in the narrow spaces between the massulae. 



In Salvinia the microsporangia arise as branches from spo- 

 rangiophores which bud out from the columella, so that their 

 number much exceeds that of the macrosporangia, or of the 

 microsporangia of Azolla. There are no separate massulae. 





Fig. 243. — Marsilia vestita. A, Fruiting plant of the natural size; sp, sporocarps; B, 

 a single sporocarp, X4; C, cross-section of the same, Xs; D, germinating sporo- 

 carp, showing the gelatinous ring by whkh the sori (s) are carried out, X3. 



and in the macrosporangium the epispore is much less developed 

 than in Azolla. 



The MarsiliacetE 



The two genera of the Marsiliaceae, Marsilia and Pihdaria, 



are much more closely related than Salvinia and Azolla, and at 



the same time their resemblance to the homosporous Ferns is 

 27 



