THE FIBRO-VASCULAR SYSTEM AND ITS FUNCTIONS. 



37 



to appreciate the extensive distribution of the vascular system. It is not simply the developing 

 seeds, with the case containing them, which require to be nourished, as in ordinary fruits, but also 

 the much larger mass of tissue outside of that, constituting the flesh. So much growth has to be 

 made in a comparatively short time that the apple tree has to store up the necessary material 

 during the previous season, for the early spring growth. The short branches, known as fruit-spurs, 

 bear the fruit-buds, which are plump, and well nourished, in order to give rise to the blossom. The 

 material stored up in the branches is passed on to the flowers when they are fertilized. It is easy 

 to tell, within a few days, when fertilization has occurred, for the flower-stalk stiffens and begins 

 to swell. This stiffening and thickening are due to the rush of food-materials, and after the fall 

 of the petals the stored-up food is practically exhausted. Then the young apple is partly 

 nourished by the parent-plant, with its fresh green leaves, and partly by its own exertions. The 

 water, containing mineral matter in solution, enters from the soil, passes along the roots, and up 

 the stem, until it reaches the fruit-spurs. Here it enters through the stalk of the fruit, and is 

 distributed along the various channels, until it bathes the tissues wherever the fine network 

 reaches. 



The amount of water contained in a ripe and sound apple is 84 per cent., on an average,, so 

 that a proper water supply is all-important for the formation of the fruit. The fruit increases in 

 size, not so much from the multiplication as from the enlargement of the cells, and it can readily 

 be understood how nicely the balance must be adjusted, in order to regulate the supply. The 

 water-stream will be directed along the main channels towards the apex of the fruit, and if the 

 cells are overgorged, then the vascular network may not be able to keep pace with the expanding 

 cells, and if there is a dearth of water, a concentration of the contents of the cells may 

 follow. 



The leaves of the tree, under the influence of sunlight, are now busy manufacturing starch, 

 some of which will be transported in the soluble form of sugar to nourish the growing fruit, which 

 is, however, able to a certain extent to provide for its own needs in this respect. The 

 chlorophyll-containing cells of the hypodermal layer are also producing starch, under the influence 

 of sunlight, so that, from these two sources — the green leaves and the green layer of the fruit — 

 abundance of starch is formed in a normal season. This has to be rapidly transported, when the 

 fruit is swelling, from the place of manufacture to the tissues, where wanted. The insoluble starch 

 is rendered soluble by means of a ferment ; and the use of the innumerable connected and branching 

 veinlets in the hypodermal tissue will now be evident. In the fruit-growing season there is a 

 great drain upon the plant's resources, and the manufactured starch must be quickly removed, 

 in order to make room for fresh supplies, for, as Pfeffer remarks, " The solution of starch is 

 hastened by the continual removal of the sugar produced." 



But the green apple is not merely a consumer, using the material supplied for building up 

 its tissues ; it requires to store up material towards the period of ripening, and starch grains are 

 invariably found in the cells of unripe fruit. According to Browne (102), "The percentage of 

 starch in apples varies entirely with the age of the fruit ; in green apples it may amount to 5 per 

 cent, or more, while in the completely-ripened fruit it is altogether wanting." 



The vascular bundles, as a whole, can now be understood. In a transverse section of 

 the stalk, just as it enters the fruit, there are ten vascular bundles, although sometimes two 

 adjoining may become confluent. (Fig. 95.) These, on entering the fruit, spread out to form 

 ten main trunks, with numerous branches (Fig. 89), and conveniently situated about midway 

 between the skin and the centre. The earliest branching and the most direct course is towards 

 the carpels and the seeds, then the flesh is supplied by numerous diverging branches, which unite 

 to form a network of vessels, and finally terminate beneath the skin, in a perfect maze of the 

 most delicate forked veinlets. So richly is the apple supplied with a connected system of vascular 

 bundles that it would be difficult to find an area of any size without them. 



