8 SCIENCE AND FRUIT GROWING 



the leaves : then a cork cambium forms across the base of the 

 leaf-stalk at the junction with the branch, and a few layers of 

 cork, called the separation layer, isolate the leaf. The dead 

 leaves may hang on for some time, but high winds, or the first 

 touch of frost, will bring them off, leaving the scar already healed 

 over by the layer of cork. 



FLOWER. The usual method of plant-reproduction is by 

 seeds, and flowers are necessary that these may be produced. A 

 complete flower (Fig. 4) consists of calyx, corolla, stamens and 

 pistil, but only the last two are really necessary in order that seeds 

 may be formed. The calyx and corolla are essentially protective 

 in their nature, and guard the delicate reproductive organs inside. 

 The corolla, also, is frequently brightly coloured, in order to 

 attract insects for effecting fertilisation, without which no seed 

 can develop. 



The undeveloped seeds or ovules are contained in the ovary at 

 the base of the pistil. Above the ovary is the style, bearing at 

 its summit the stigma, which has some part of its surface specially 

 adapted to catch the pollen grains, which appear as a yellow dust 

 on the stamens, and are carried to the stigma by insects, wind, 

 or in some other manner. When a pollen grain reaches a 

 receptive stigma, the former puts out a tube which penetrates 

 the style below, enters the ovary, and makes its way to the 

 ovule. The contents of the pollen grain pass down the tube, 

 and fuse with part of the ovule (the egg cell), thus effecting 

 fertilisation. Changes then occur, the ovary and ovule develop 

 more or less rapidly, and, finally, the fruit and seeds become 

 fully formed. Sometimes other parts of the flower help to form 

 the fruit, as in the apple, where the receptacle, or top of the 

 flowering stalk, develops to form the fleshy part of the fruit. 



From this it will be evident that the seed which is formed, being 

 the product of the fusion of the male and female elements, will, 

 as in the case of animals, produce an individual resembling, 

 but by no means identical with, the parents : resemblance to the 

 female, indeed, is often very remote, inasmuch as flowers df culti- 

 vated fruit trees are often self-sterile, that is, they can only be 

 fertilised by pollen from a different variety. Where large 

 plantations of any one variety of apple, pear or plum are grown, 

 it is generally necessary that every third or fourth tree be of some 

 different variety, in order to ensure fertilisation. 



Cultivated varieties of fruit trees cannot, therefore, be propa- 

 gated by sowing the seeds produced, and they have to be multi- 

 plied by grafting, or budding, operations wherein a shoot, or 



