DEVELOPMENT OF PLANTS 309 



in the lower ferns and Filicales, and fertilization is effected in 

 the same manner. 



(d) The Germination of the Gametospore. — The most note- 

 worthy departure in the germination of the gametospore is seen 

 in the limited growth of the stem. The early stages are similar 

 to those of the Filicales, but after the stem has formed a few 

 nodes with three leaves each, it is replaced by a stem that devel- 

 ops at its base. This second stem attains a somewhat larger size, 

 but is finally replaced in the same manner by a third shoot. In 

 this way several stems are formed until finally one is developed 

 that penetrates the ground and forms the characteristic rhizome 

 of the mature sporophyte. These plants with their scale leaves 

 reduced to protective organs, sunken stomata and chlorenchyma 

 confined to the grooves of the internodes, present an extreme 

 form of xerophytic structure and form a sharp contrast with the 

 large and usually thin-leaved Filicales. While they occur in dry 

 localities, to which conditions their structures admirably adapt 

 them, they are of more common occurrence in moist and wet 

 places. This peculiar distribution of the species of Equisetum 

 has not been explained. It is evident that these plants, like the 

 rushes and sedges of our marshes and shallow ponds, are often 

 exposed to intense heat and light, which would cause an exces- 

 sive transpiration. Possibly these plants are not able to absorb 

 water rapidly owing to the limited amount of conducting tissues 

 and to the exclusion of the atmosphere by the water which sur- 

 rounds the roots (see pages 40, 46), consequently they are at 

 the same disadvantage and require the same protective devices 

 as plants living in arid localities. 



Order 4. Lycopodiales. The Club Moss Ferns 



115. General Characters. — The members of this group are 

 popularly known as the club moss ferns owing to their small 

 moss-like leaves and the arrangement of the spore-bearing leaves 

 into club-like strobili or cones (Fig. 236). The gametophyte or 

 sexual generation is also suggestive of the mosses. Particularly 

 is this true of the male gamete, which is small and apparently 

 biciliate (Fig. 240). 



