STUDIES OF SEED-PLANTS 207 



before petals did. Moreover, the fact that sometimes green 

 petals are found does not prove that petals were once green 

 leaves. Also, colored sepals and bracts were not once petals. 

 But the fact that sepals, petals, stamens, and pistils all suggest 

 more or less similarity to leaves probably means that they 

 have developed or been evolved from expanded leaf-like 

 structures in lower plants and that foliage leaves have de- 

 veloped from similar structures. 



202. Flower Regarded as Shortened and Modified 

 Branch. Every flower begins as a set of leaf-like structures 

 arranged in whorls or circles on the receptacle, which is 

 simply the conical end of the flower-stalk. As the sepals, 

 petals, and stamens grow up, the receptacle may remain 

 conical (as in Fig. 63, A), or the receptacle may become more 

 or less cup-shaped, resulting in flowers like B and B f in Fig. 63. 

 And if the receptacle both grows cup-shaped and at the same 

 time closely surrounds the ovary, the result is a flower like 

 Fig. 63, C, in which the ovary is beneath the sepals and petals. 



203. Stamens are usually entirely free from each other, 

 but in some flowers they are united either by the anthers or 

 by the filaments into a ring, and in some flowers into two or 

 three groups or more. In the bean flower there are two groups, 

 with nine stamens in one, and one in the other. In the dande- 

 lion ( 207) the stamens are united into a ring, which sur- 

 rounds the pistil. 



The anther is the essential part of the stamen. In order 

 to get acquainted with some of the various forms of anthers, 

 they should be carefully examined in the flowers studied. 

 Use a hand-lens, and also remove some pollen for examina- 

 tion with the compound microscope. 



Anthers are in some flowers attached directly and without 

 filaments. They are then said to be sessile, just as a leaf 

 attached without a petiole is sessile. 



(D) Germination of pollen-grains and growth of pollen-tubes may 

 be studied by placing some pollen, if possible from several kinds of 



