510 



INTRODUCTION TO CETPTOGAMIC BOTANY. 



and the inner is elongated and protruded (Fig. 14<, a), and at 

 length by cell-division expands into a thin marchantioid frond 

 or prothallus. On the under side of this two kinds of bodies 

 are formed, one of which produces spiral ciliated spermatozoids 

 (Fig. Ill); the other are archegonia sunk in the cellular tissue, 

 resembling those of Muscales. These were first described by 

 Nageli, and have since been frequently recognised. Leszczyc- 

 Suminski witnessed the entry of the spermatozoids into the 



Fig. 111. 



Spermatozoids of Pteris aquilina, 

 after Thuret. 



Fig. 112. 



Aetiniopteris radiata. 

 a. Part of ring, magnified. 

 6. Spore, magnified. 



archegonia, and, impressed with the Schleidenian theory of 

 impregnation in Phsenogams, believed that the broader end 

 was changed into a young plant, of which the radicle was 

 directed towards the base of the archegonium, a direction 

 exactly contrary to that which prevails in Phsenogams. It is 

 now, however, ascertained that the cell at the base of the 

 archegonium, after impregnation, gives rise to the new plant. 

 This is gradually developed, and is of different duration in 

 different species. Wherever it is perennial, however, it bears, 

 year after year, a new crop of sporangia without any further 

 impregnation. The impregnation takes place only in the 

 archegonia of the prothallus. No successive crops of arche- 

 gonia are formed, as in mosses. 



572. It was stated under mosses, that there is no good rea- 

 son to believe that the parts of the peristome are modified 

 leaves. There does not seem the same objection in Ferns to 

 the sporangia being altered fronds, provided the ring be not 

 supposed to represent the mid-rib, which is plausible enough 

 where it forms a great circle, but not where it is apical or very 



