502 MOSSES AND FERNS CHAP. 



formed. The archesporial cells rapidly divide, but show little, 

 regularity in the divisions. All of the resulting cells separate 

 and produce four spores in the usual manner. The wall of the 

 mature sporangium consists regularly of three layers of cells, 

 of which the innermost is the tapetum. The tapetum bound- 

 ing the lower part of the archesporium is derived from the 

 cushion-like group of cells below it, to which Bower gives the 

 name "sub-archesporial pad." The tapetum does not become 

 disorganised, as in most Ferns and Equisetum, but remains 

 as part of the sporangium wall. The fully-grown sporangium, 

 as in all species of Lycopodium, is kidney-shaped. 



Among the numerous other species investigated by Profes- 

 sor Bower, L. clavatum represents the type most widely re- 

 moved from L. selago. The differences between the two are 

 summarised by Professor Bower as follows : 



"i. The sporangium is similar in position and in general 

 form to that of L. selago, but its body is more strongly curved. 



"2. The archesporium here consists of three rows of cells, 

 each row being composed of a large number (about twelve) 

 of cells ; thus the extent of the archesporium is much greater 

 than in L. selago, occasional additions to it seem to be made 

 by cells cut off periclinally from the superficial cell at an early 

 stage. 



"3. The tapetum is similar in origin to that in L. selago. 



"4. The sub-archesporial pad is much more developed, and 

 is at times extended as processes of tissue which penetrate the 

 sporogenous mass for a short distance. 



"5. The stalk of the sporangium is much shorter and 

 thicker than in L. selago. 



"6. Arrested sporangia are frequently present, and may be 

 found either at the base or apex of the strobilus. 



"7. L. inundatum may be looked upon as an intermediate* 

 link between the type of sporangium of L. selago and that of 

 L. clavatum, both as regards form of the sporangium and com- 

 plexity of the archesporium." 



Phylloglossum 



The other genus of the Lycopodiacese contains but the single 

 species P. Drummondii, from Australia and New Zealand. 

 This curious and interesting little plant has been carefully in- 



