378 



PLANT MORPHOLOGY 



parts have arisen but, of course, in their proper place between the sepals 

 and stamens (Fig. 322). This flower, when mature, has small petals. 

 In the fleabane {Erigeron) and other members of the Compositae the 

 sepals are the last members to appear. They remain vestigial. This 

 flower shows the epigynous type of development (Fig. 323). 



Fig. 323. Floral development in fleabane (Erigeron). A, very young and older inflores- 

 cence, the flowers arising on the convex receptacle, X75; B to E, successive stages in the 

 development of a single flower, X200; b, bract; fl, flower; p, corolla; st, stamen; c, carpel; 

 s, calyx. 



The Stamen. The stamen of angiosperms is the same structure as in 

 gymnosperms, a microsporophyll. Generally it is differentiated into a 

 terminal, club-like, spore-bearing portion, the anther, and a slender stalk, 

 the filament (Fig. 318B). A cross section of a young anther usually shows 

 four microsporangia, but the number may vary among different angio- 

 sperms from one to many (Fig. 32-iA). As a rule, the microsporangia 

 extend the entire length of the anther. Later, by the breaking down of 

 the intervening tissue between each pair of microsporangia, two large 

 cavities may be formed (Fig. 3245) ; or the four microsporangia may 



