410 



SYSTEMATIC BOTANY. 



tative manner. This important discovery, however, cannot alter 

 our views on the alternation of generation in Vascular Cryptogams, 



Reproduction of Ferns: , spore germinating; 6, more advanced (magn. 50 diam.); c, full- 

 grown prothallium, with archegonia (lower surface) ; d, vertical section of the central 

 region of a prothallium, passing through an archegonium and two antheridia; e, two 

 antheridia (side view) ; f, antheridia seen from above ; g, antheridium burst (side view) ; 

 k, sperm-cell from antheridium; i, spermatozoid escaping from sperm-cell (magn. 300 

 diam.); k, front view of a spermatozoid; I, vertical section of a young archegonium; 

 w, more advanced ; n, still older, with the canal open and an embryonal corpuscle in 

 the sac (magn. 100 diam.); o, view of the mouth of an archegonium, from above; p, 

 vertical section of an archegonium with the embryo in course of development in the 

 sac; q, the same, more advanced (less magnified); r, vertical section of young plant, 

 more advanced, with a fragment of the prothallium (magn. 50 diam.); s, t, young 

 plants of Pteris serrulata, with their first and second leaves and adventitious roots 

 still connected with their prothallia. 



for such an exception cannot, from its abortive nature, destroy the 

 rule. 



In the Muscinece the alternation of generations is similar to that 

 in Vascular Cryptogams. Out of the germinating spore (in all 

 Mosses and in some Hepaticce) comes a Protonema of a thread-like 

 structure, on which the sexual organs are formed, or (as in 

 most Hepaticce) the sexual generation is directly developed. It 

 is worthy of notice that recently Drs. Pringsheim and Stahl have 

 succeeded in bringing about an artificial production of the Proto- 



