72 



STRUCTURAL BOTANY 



It now at once begins to grow and divide, becoming the 

 embryo, or young plant, of the sporophyte generation. 



The embryo of a Fern differs from that of the plants 

 hitherto described, in having no suspe.nsor ; the whole of 

 the fertilised ovum goes to form the embryo. Through- 

 out the whole of the Fern-group there is considerable 



uniformity in the 

 development of 

 the embryo from 

 the ovum. The 

 first wall (called 

 the basal wall) 

 runs nearly par- 

 allel to the axis 

 of the arche- 

 gonium, and at 

 right angles to 

 the axis of the 

 whole prothallus. 

 This divides the 

 young embryo 

 into an epibasal 



FIG. 37.-Embryo of a Fern (Pteris] in median and ft ^pobasal 

 section, s, apex of stem ; e, first leaf ; r, root ; 9f 



f, foot by which embryo is attached to pro- half ; the former 



Hofme S isteo r thallUS ' Magnifiedl5 ' (After faces the apex 



and the latter the 



base of the whole prothallus. Two more cell-walls then 

 appear, all three being at right angles to each other, so 

 that the embryo is now cut up into eight parts or octants. 

 From the epibasal half the apex of the stem and the 

 first leaf arise, while the hypobasal part produces the 

 apex of the root, and an organ called the foot, which is 

 of a temporary character and serves to attach the young 



