FILICJNEAE.—HE TEROSPOR US FTUCINEA E 



229 



Ferns, we shall nevertheless describe them together in this place on account of the 

 many points which they have in common in their life-history. 



The first or sexual generation {pophore, oophyte) of the heterosporous Ferns is 

 developed from two different kinds of spores ; the small spores produce only sperma- 

 tozoids and are therefore of the male sex ; the large spores, which are several hundred 

 times larger than the others, produce a small prothallium which never separates from 

 the spore and forms one or more archegonia; the macrospores may therefore 

 themselves be said to be female. 



The microspores produce a very rudimentary prothallium and an antheridium. 



Fig. 182. Salvinia natans, A an entire microspo- 

 rangium with microspore-tubes st bursting through it 

 B one of these tubes st issuing from the envelope /; of 

 the microsporangium. a the antheridium still closed. 

 C tube with empty antheridium. D spermatozoids. After 

 Pringshemi. A magn. about too, B 200, D 500 times. 



Fig. 183. Marsilia Salvatrix. A a macrospore sp with its mucilaginous envelope si and the apical papilla 

 projecting into its funnel and enclosing a broad yellowish drop ; sq the ruptured wall of the macrosporangium. 

 B a microspore which has burst and discharged the spermatozoids ; ex the exosporium, dl the protruded endosporium 

 containing granules, zz the spirally twisted spermatozoids, yy their vesicles with grains of starch. The gelatinous 

 envelope of the inicrospore has disappeared; the exosporium does not show the arrangement of the protuberances 

 which is incorrectly indicated in the figure. A magn. about 300, B 550 times. 



In Salvinia they are imbedded in a mass of hardened granular frothy mucilage which 

 fills the entire microsporangium, and are not discharged from the sporangium, but 

 each of them puts out a tube from its endosporium which pierces through the 

 mucilage and the wall of the sporangium, and forms a transverse septum at its 

 curved extremity (Fig. 182 ^ and E); the cell thus formed at the extremity of the 

 tube divides by an oblique wall, and the two cells represent the antheridium, while 

 the lower cell (Fig. 182 st) must be considered to be the prothallium reduced to a 



