LEPTOSPORANGIATJE HETEROSPORE^ 



417 



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

 confined to the outside of the massulse, 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 massulse. 



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 massulse, 



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

 a -single sporocarp, X4; C, cross-section of the same, X5; D, germinating sporo* 

 carp, showing the gelatinous ring by which the sori is) are carried out,X3. 



and in the macrosporangium the epispore is much less developed 

 than in Azolla. 



The Marsiliace^ 



The two genera of the Marsiliacese, Marsilia and Pilularia, 

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

 the same time their resemblance to the homosporous Ferns is 

 27 



