54 SURVEY OF THE REPRODUCTI\^ PROCESS 



the case in the latter order, or in the same one, as is the 

 common rule in ferns. On the other hand, the proto- 

 morphic stage, which is so much protracted in Hepaticae, 

 and still more in mosses, is represented in ferns only by the 

 confervoid chain of cells, termed the suspensor, which is the 

 first result of the development of the impregnated germ, 

 and at the farther end of which the embryo is formed. 



In both groups the impregnated archegonial cell germi- 

 nates while still within its receptacle, so that the resulting^ 

 growth has the appearance of being simply an expansion of 

 the structure immediately preceding ; thus the theca^ of the 

 moss simulates a mere out-gTOwth from the parent axis, 

 while the prothallium, which is also really the parent of the 

 fern-stem, has been described as its primordial leaf or 

 cotyledon, from its resemblance to that organ in the higher 

 plants ;* for as the embryonic structure advances, it sends 

 downwards rootlets into the earth, and upwards a fern 

 stem — the centre of growth still remaining in the prothallial 

 frond. 



The continuity of the organization is not broken in upon 

 by any act of the nature of " seeding," till the dispersion of 

 the spores. These particles, though physiologically equi- 

 valent in the two groups — inasmuch as in both they are 

 a*g^exual gemmae, and not the direct products of impregna- 

 tion — thus come to have very different homologies ; for 

 they belong in one case to the protomorphic stage, and 

 germinate more or less directly into the leafy axis, while in 

 the other they are gamomorphic gemmse from that axis, 

 and develope the prothallium or sexual phj^oid. 



On the assumption of the line of homology now indicated, 

 we may establish a parallel between the separate fern-fronds 

 and the leafy shoots of the moss — observing that in both 

 orders alike, free gemmae are occasionally detached for the 



* Carpenter Compar. Phys. 4tli Ed., p. 507, Note. 



