210 BOTANY. 



velop. After fertilization the germ-cell gives rise directly 

 to a leafy plant, which emerges from the spore-wall in a 

 way to remind one very forcibly of the growth of a plantlet 

 from a seed. This resemblance is made greater by the 

 likeness the first leaves bear to cotyledons (Fig._119). 



But one genus, Selaginella, Is known in this order. It contains 

 about three hundred species, most of which are tropical. Two only 

 (viz., S. rupestris and S. apus) are common tliroughout the United 

 States, although five others are indigenous. Several exotic species 

 are commonly cultivated in plant-houses, 



441. The ftuillworts {Order Isoetacece) are small grass- 

 like plants, with narrow leaves growing from short, thick, 

 tuber-like stems. They grow in water or muddy places, 



442. Their spores, which are of two kinds, are produced 

 in spore-cases on the upper surfaces of the leaf -bases. In 

 their germination and development of the sexual organs 

 they resemble the plants of the previous order. 



The Quillworts are all of one genus, Isoetes, of which 

 there are in the United States fourteen species. 



Fossil Lyeopods. — Two orders of Lycopods once existed, containing 

 large trees, which appear to have been very abundant. The Lepido- 

 dendrids (Order Lepidodendracese were a metre (3 to 4 feet) thick 

 and 15 to 20 metres (45 to 60 feet) high, and seem to have had the 

 general appearance of the Club-mosses. The Sigillarids (Order Sigil- 

 lariacese) appear to have been trees 30 or more metres (100 feet) in 

 height and li metres (4 or 5 feet) in diameter. Both produced two 

 kinds of spores, showing their relationship to the Little Club-mosses 

 and the Quillworts. Although very abundant in the Coal Period, 

 they have long since become entirely extinct. 



P)-aeiical Studies. — (a) Secure a few fresh or alcoholic specimens 

 of various kinds of Lycopods in fruit. The Little Club-mosses may 

 be readily obtained in plant-houses. Make cross-sections of the stems 

 and study the flbro-vascular bundles, which in Lycopodium are im- 

 bedded in a thick mass of fibrous tissue. Examine the leaves, noting 



