346 EMBRYO OF LYCOPODIUM 



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 tissue 

 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 in 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 in part 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 seed plants. 

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

 single genus, Selaginella, 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 southw^estern 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 trans- 

 lucent, so that the green color of the chloroplasts can be seen. 

 These reactions occur even in the dead plants and so create the 

 impression that they have returned to life. Many of the species 



