314 THE SELAGINELLACEAE 



continue on through the seed plants. The gametospore enlarges 

 and divides into two cells by a transverse wall. The outer of 

 the two daughter cells takes no part in the formation of the 

 sporophyte, though elongating and often dividing several times. 

 These cells are termed the suspensor (Fig. 240, s) and function 

 in pushing the lower daughter cell down into the nourishing tis- 

 sue of the gametophyte. The lower daughter cell, by a series 

 of divisions that at first resemble the common ferns, forms the 

 young sporophyte. This consists of a stem with one or two 

 cotyledons, a massive foot and finally, at a late period in the 

 development of the sporophyte, of a root (Fig. 240). The tardy 

 development of the root has been cited as an indication of the 

 origin of the lycopods from very primitive ancestors, in which 

 the formation of the root had not become established. It may 

 also be due to the abundant food stored in the gametophyte and 

 hence the development of the root might well be delayed until 

 this store is exhausted. The growth of the sporophyte is very 

 slow and it remains as a parasite upon the gametophyte for a 

 long time, even for years in some of the subterranean forms 

 (see Ophioglossales). The elongation of the stem and root is 

 effected by the division of several cells rather than by one apical 

 cell, as in previous cases, a feature to be noted in the following 

 division. 



117. Family 2. Selaginellaceae. This family includes but a 

 single genus, SelagineUa, of over 600 species. Only a few forms 

 occur in the temperate regions, the majority being confined to 

 tropical countries, where they often form one of the most attrac- 

 tive features of the forest vegetation owing to the symmetry of 

 their branching and the rare delicacy of their foliage (Fig. 241). 

 For these reasons they are extensively cultivated and familiar 

 objects in conservatories and florists' shops. The so-called res- 

 urrection plant, Selaginella lepidophylla, lives in the very arid 

 sections of the southwestern United States, and during drought 

 reduces its surface to a nest-like ball by rolling up its branches 

 into tight coils. In this condition it appears as < a brownish dead 

 mass. When moistened, the absorption of water causes the 

 branches to quickly uncoil and also renders the tissues translu- 



