FERNS. 



269 



attaches the embryo to the prothallium, and transports nourishment for the 

 embryo until it can become attached to the soil and lead an independent ex- 

 istence. During this time the wall of the archegonium grows somewhat to 

 accommodate the increase in size of the embryo, as shown in figs. 312, 313. 

 But soon the wall of the archegonium is ruptured and the embryo emerges, 

 the root attaches itself to the soil, and soon the prothallium dies. 



The embryo is first on the under side of the prothallium, and the first leaf 



Fig. 3". 

 Two-celled embryo of Pteris serrulata. Remnant of archegonium neck below. 



and the stem curves upward between the lobes of the heart-shaped body, and 

 then grows upright as shown in fig. 314. Usually only one embryo is formed 

 on a single prothallium, but in one case I found a prothallium with two well- 

 formed embryos, which are figured in 315. 



559. Comparison of ferns with liverworts and mosses. In the ferns then 

 we have reached a remarkable condition of things as compared with that 

 which we found in the mosses and liverworts. In the mosses and liverworts 



