THE CLUB-MOSSES 187 



the cones of Lepidodendron already described. 

 The sporophylls are of the usual shape, and on 

 the upper side of each is seated a large sporan- 

 gium, attached by its under side to the long 

 basal portion of the fertile leaf. A ligule is pres- 

 ent in the usual position. But at this stage 

 there is already a striking peculiarity. Almost 

 the whole cavity of the sporangium is occupied 

 by a single megaspore, of enormous dimensions, 

 with its membrane in contact, or nearly so, with 

 the wall of the sporangium. Side by side, how- 

 ever, with the one megaspore which reached 

 maturity, are found three abortive spores, its 

 undeveloped sister-cells; evidently the original 

 number of megaspores in a sporangium was 

 four, of which one had gained the upper hand 

 over the rest. The same thing occurs occasion- 

 ally in Selaginella, and regularly in the hetero- 

 sporous Water-ferns; analogies are also to be 

 found in the development of the embryo-sac of 

 recent Seed-plants. 



At a later stage the seed-like condition was 

 complete. A thick envelope had grown up from 

 the sporophyll, and formed a close investment 

 round the sporangium, only leaving open a nar- 

 row crevice along the top; this crevice may be 

 called the micropyle, but it had the form of a 

 long slit, extending the whole length of the 

 sporangium. When cut across, the appearance 



