330 HOW PLANTS LIVE AND WORK. 



III. — Fertilisation Devices. 



We have seen that, wonderful as is the life-work of the roots, 

 the stem, and the leaves of a flowering plant, that of the flowers 

 themselves is much more so. We have traced out in its very 

 broadest outlines the work done by sepals, petals, stamens, and 

 pistil in the Wallflower, and have found that each part of the 

 blossom has a definite duty allotted to it. The calyx protects the 

 flower-bud, and, when the bud has opened, forms pockets for the 

 storage of honey. The corolla, by its odour, and by hanging out 

 gaily coloured placards, advertises the presence of the honey. 

 The stamens produce fertilising pollen, and the pistil contains 

 fertilisable ovules. The relative positions of these parts render it 

 practicall} certain that in obtaining the honey the bee must 

 become dusted with pollen in those parts of its body which are 

 likely to come in contact with the sticky stigma of the next Wall- 

 flower visited. In those flowers whose ovules are contained in 

 ovaries, the access of pollen to the stigma must take place before 

 fertilisation can be effected. Nature has adopted all sorts of 

 wonderful devices to secure that the ovules shall be fertilised by 

 pollen from different flowers, for " breeding in and in " is as 

 ruinous among plants as it is in animal life. 



We must now deal with the most noteworthy of the devices 

 adopted by plants to prevent self-fertilisation. One extremely 

 common method is to have stamens and pistils on different 

 flowers, and it is immediately obvious that with such an arrange- 

 ment self-fertilisation is, in the nature of things, an absolute 

 impossibility. It is quite true that such flowers in many cases 

 depart very widely from one's previously conceived idea of what 

 constitutes a flower. If in early Spring we go out into the woods, 

 and fix on an old Oak tree (an Oak hardly ever " fruits '' before it 

 is fifty years old), we shall very likely see the flowers on some of 

 the young twigs. The female flowers, one to five on each flower- 

 stalk, are near the end of the twig, while the male flowers arise 

 lower down. Each female flower consists practically of a single 

 pistil, partially enclosed in two envelopes. With the envelopes 

 we need not here trouble ourselves, except to remark that the 

 lower one ultimately becomes the familiar " cup " of the acorn. 

 What more immediately concerns us is the fact that the stigma 



