72 



Elementary Work in Botany. 



an organ ceases to be useful it becomes rudimentary, and 

 finally entirely disappearing it is said to be obsolete. For 

 example, when flowers grow in clusters, to form larger 

 signals, and to make it easier for their insect aids, thus 



summoned, to gather nectar, the 

 subtending leaves doing more 

 harm than good are reduced to 

 bracts, or become obsolete, as in 

 most plants of the mustard family. 

 When an improved condition of 

 a flower lessens the amount of pol- 

 len required, one or more stamens 

 become rudimentary or obsolete. 

 Thus, in sage, as shown in Fig. 

 52, by an ingenious modification 

 of two stamens they are made as 

 effective as were the original five. 

 The iiseless ones are obsolete.* 



Promoted and Degraded Or- 

 gans. In a few cases when incon- 

 spicuous flowers are gathered into 

 heads some of their subtending 

 leaves, instead of being degraded 

 to the condition of bracts, are pro- 

 moted to fill the office of petals. Thus the corolla-like 

 involucres of dogwood and anemopsis are formed (Fig. 80). 



*In some native sages two of the three upper stamens are rudimentary; but 

 the middle one directly in the way of the style is obsolete. In most irregular 

 flowers only the upper stamen is rudimentary or obsolete. 



Fig. 52. Mechanism for securing 

 cross-fertilization in the common 

 garden sage. a. The flower as it ap- 

 pears when the anthers are ready to 

 give up their pollen. The stigma not 

 yet ready to receive pollen shows its 

 two lobes protruding from the tip of 

 the upper lip of the corolla, b. A 

 flower visited by a bee, who receives 

 the pollen on his back while sipping 

 nectar from the bottom of the corolla. 

 C. Shows the position of one of the 

 pair of stamens which stand at the 

 mouth of the corolla, d. The anther 

 cell which yields pollen, e. The 

 ab jrtivecell, which is pushed back- 

 ward by the bee as he enters, thus 

 bringing the other cell down upon 

 his back as shown in b. f. The 

 stigmas, g. The base of the filament. 

 A. Shows the stamens as seen from 

 the front. B. A side view of one 

 stamen. It is plain that pushing to 

 the left would cause d to descend by 

 turning on its joint at h. 



