130 The Flower 



is the pistil. Its lower end is swollen to form the 

 ovary and contains the ovule, a little round green 

 body, which will later on ripen into the seed, the horse- 

 chestnut you know so well. 



Most ordinary flowers show these four parts, although 

 the numbers in each ring vary a great deal according to 

 the kind of flower. In some flowers, however, you will 

 find that the calyx or the corolla is missing, and even 

 sometimes, as in the catkins, that neither is there. 

 Neither calyx nor corolla is really necessary to the 

 flower although they make it more conspicuous and 

 protect the important parts inside from rain and wind. 

 These important parts are the stamens and pistil, for if 

 some of the pollen either from the same flower or from 

 another flower of the same sort does not fall into the 

 pistil and so fertilise the flower it will all wither away 

 without forming any seed. The pollen consists of a large 

 number of very tiny yellow grains. As soon as one of 

 these grains reaches the top of the pistil it begins to 

 send out a tube which looks, under a microscope, not 

 unlike the root of a seed when it first begins to germinate. 

 This tube grows right down through the pistil until 

 it touches the ovule. This, as it were, Avakes the ovule 

 up, and it begins to swell together with the ovary 

 surrounding it, until in time the ovule becomes the seed 

 and the ovary the fruit. Sometimes if we have very 

 cold weather when the fruit trees are in flower the fruit 

 instead of " setting " falls off as soon as the flowers are 

 faded. What has happened is this : the frosty weather 

 has nipped the delicate pollen tubes just as they were 

 growing and has killed them. Hence the flowers are 

 not fertilised and the fruit will not set. 



Since pollen from another flower of the same kind 



