478 MOSSES AND FERNS chap. 



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 bounding 

 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, apparently, 

 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 Professor 

 Bower, L. clavatum represents the type most widely removed 

 from L. selago. The differences between the two are sum- 

 marised 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. inundatuin 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 

 complexity of the archesporium." 



Phylloglossum 



The other genus of the Lycopodiaceae contains but the single 

 species P. Dj'ummondii, from Australia. This curious and 



^ Bovver (15), p. 521. 



