LYCOPODIALES 



321 



The germination of both types of spores may begin before they are 

 shed, but it is continued on the moist soil. The microspore first 

 partitions off a lenticular cell, which is vestigial like those in the 

 pollen-grains of Pinus, representing a male prolhallus. The rest of 

 the contents segment to form a wall of eight sterile cells surrounding 

 a numerous group of spermatocytes (Fig. 264, A). A mucilaginous 

 change appears in the walls of these latter cells. Meanwhile their 

 protoplasts form each a single curved spermatozoid, motile in water by 

 two cilia. Swelling of the mucilage by water bursts the wall of the 

 spore, and the spermatozoids escape (Fig. 264, B). 



The germination of the megaspores produces an internal tissue of 

 greater extent, which may be styled the female prolhallus. Its develop- 



A B 



Fig. 264. 

 A, microspore of S. apus after germination. B, the same just before extrusion 

 of spermatozoids. (After Miss Lyon.) 



ment begins below the meeting of the three converging ridges of the 

 tetrahedral spore, and it extends into the spore-cavity, which is stored 

 with nutritive material (Fig. 261). The increase in bulk of the 

 contents ruptures the wall of the spore along the converging ridges, 

 so that the surface of the tissue is exposed (Fig. 265, I.). Near the 

 central point the first archegonium appears, while laterally others may 

 be formed later, but not in regular succession A vertical section 

 through a megaspore of S. denticulata shows it completely filled with 

 tissue of the prothallus, while its exposed surface bears rhizoids [rh) 

 and archegonia in various stages of development {ar) (IV.). The 

 archegonium consists of a neck [n) composed of two tiers of four cells 

 each : a canal-cell [c.c), ventral-canal-cell [v. ex.), and the ovum [ov.) ; 

 all of which were derived by segmentation from a single superficial 

 cell of the prothallus (V.). When mature the neck is open, the 

 canal-cell and ventral-canal-cell have disappeared, and the ovwn, 

 which is now a rounded primordial cell, is open to access of the 



B.K. X 



