D1V, I 



MORPHOLOGY 



197 



gonium is not, as appears at first sight, a member of the moss-plant, 

 but lives on this like a parasite. It is, in fact, the spore-bearing 

 generation (sporophyte) which remains permanently attached to the 

 moss-plant (gametophyte). 



In the Pteridophyta, on the other hand, the leafy plant is the 

 sporophyte and bears small and inconspicuous sporangia, usually on 

 leaves which are termed SPOROPHYLLS. These may resemble the 

 foliage leaves, but there is often a division of labour between the 

 sporophylls and the foliage leaves. The former are devoted mainly 

 or entirely to the production of sporangia and, therefore, differ from 

 the foliage leaves in the lack of expanded green surfaces. The 

 sporophylls are often associated in numbers at the ends of branches of 



FIG. 226. Diagram of the 

 sporangium of a Pterido- 

 phyte, the sporogenous 

 tissue (sgr) being enclosed 

 by a sterile wall. 



FIG. 227. Flower of Paeonia peregrina. k, Calyx ; 

 c, corolla ; a, stamens ; g, carpels. The nearer 

 sepals, petals, and stamens are removed to show the 

 pistil formed of two free carpels. ( nat. size. 

 After SCHENCK.) 



limited growth, as in Equisetum and Lycopodium (cf. Figs. 486, 491). 

 These differ in appearance from the vegetative shoots and die off 

 after they have served for reproduction. They are known as CONES 

 or FLOWERS. THE SIMPLEST FLOWER is THUS A PORTION OF A 

 SHOOT WHICH BEARS SPOROPHYLLS. The cones of Pteridophyta may 

 have a number of sterile scale leaves at the base. 



In the Spermatophyta the sporangia are also formed in special 

 regions of the shoot or FLOWERS, all the members of which are 

 concerned with reproduction and not with the nutrition of the plant. 

 These flowers, which are homologous with those of the Pteridophyta, 

 are metamorphosed regions of the foliage shoots. They are the ends 

 of long or short shoots, the leaf primordia of which do not become 

 foliage leaves but develop as the crowded floral leaves. These have 

 the diverse forms of SEPALS, PETALS, STAMENS, and CARPELS. 



The STAMENS produce the pollen or POLLEN GRAINS in the POLLEN 

 SACS, which are special sporangia with a many-layered wall. The 



