FLOWERING PLANTS INTRODUCTORY 



107 



those described below. The plane of division separating the 

 flower into similar halves usually runs from front to back of the 

 flower ; in a few cases it lies at right angles to this. Insects visiting 

 irregular flowers are usually induced to approach the flower 

 from one particular direction. On taking up their position in 

 the flower they touch the stamens and stigmas with particular 

 parts of their body, and the arrangements for cross-pollination 

 can thus be made more precise. Details will be found under 

 the examples described. 



We may now return to the consideration of the fruit of the 

 Buttercup (Fig. 59), which was seen to be derived from the group 

 of carpels after the other parts 

 of the flower have fallen. The 

 carpels enlarge, as do the young 

 seeds within them, and the seed 

 practically fills the whole space 

 within the carpel. When ripe 

 the seed is protected by the 

 firm dry carpel. The product 

 of development of the whole 

 pistil may here be called the 

 fruit, and that of the separate 

 carpels fruitlets. The latter at 

 maturity become detached from 

 the receptacle and are shed 

 singly. Since each fruitlet has 

 only one seed within it, the wall does not burst open to liberate 

 the seed, which remains, until germination, protected by the 

 carpel. 



The seed of the Buttercup (Fig. 59) consists of a covering 

 called the seed coat, a mass of food material and a very small 

 embryo plant. Under suitable conditions of moisture and warmth 

 the little plant commences to grow ; the seed is said to germinate. 

 Growth is at first at the expense of the food material stored 

 beside the embryo in the seed. When the first roots have pene- 

 trated the soil, and the first leaves are exposed to the light, the 

 little plant can obtain and manufacture food for itself. 



From what was said above, as to the differences between the 



FIG. 59. A, Fruit of Buttercup ; B, single 

 fruitlet cut in half, showing the seed in 

 which the embryo plant and the mass 

 of food material can be distinguished. 

 (After Baillon.) 



