THE STRUCTURE OF THE FLOWER 323 



nothing directly to do with reproduction, but at the same time 

 are of great indirect value in connection with it. The perianth 

 leaves may be all alike (cf. Crocus, Text-fig. XXX.), or they 

 may be differentiated into two series : an outer, known as the 

 calyx, and an inner, the corolla (cf. Buttercup, Text-fig. XXVI.). 



The individual members of the calyx are called sepals. 

 They are commonly green, and more nearly resemble ordinary 

 foliage leaves than do any other of the parts of the flower. 

 In some cases, as in the Rose, they may be remarkably leaf-like. 

 The purpose which they serve in the economy of the flower is 

 that of protection. In the bud, they commonly enclose all 

 the other floral parts. The corolla consists of petals, which 

 usually differ from the sepals in being larger and more delicate 

 in texture, and either white or gaily coloured, instead of green. 

 Like the sepals, they enclose and protect the rest of the flower, 

 but in a very large number of cases they have another and more 

 special function namely, that of attracting insects to visit the 

 flower, for a purpose to which we will return later. 



Immediately within the petals, we meet with the first of the 

 " essential organs " of the flower namely, the group of stamens 

 constituting the androecium. Each stamen consists of a 

 slender stalk or filament, terminating in a head or anther 

 of four little sacs, two on each side of the connective, as 

 the top of the filament is called. The stamen, like the other 

 parts of the flower, may be regarded as a metamorphosed leaf. 

 In some flowers, such as that of the White Waterlily, the 

 leafy nature of the stamens is particularly obvious. The 

 object of the stamen's existence is the production of the yellow 

 dust, known as pollen, with which the anther sacs are filled. 

 When the stamens are ripe, the anthers open in various ways, 

 and the pollen escapes. The stamens are the male organs, 

 and the pollen gives rise to the male gametes or sperms, without 

 whose aid no seeds can be set. We will return to the subject 

 of the fate of the pollen after considering the pistil. 



