36 



BITTER PIT INVESTIGATION. 



But these vascular bundles in the apple are continued from the stalk, and, when a transverse 

 section is made of the stalk, the ten bundles are seen arranged in the form of a cylinder (Fig. 96). 

 Sometimes, adjoining bundles have coalesced, but they are sufficiently distinct to be recognised 

 (Fig. 95). The number of vascular bundles in the fruit are determined by those in the stalk, for, 

 when an apple was found with only four carpels, there were only eight bundles in the stalk. 



In a longitudinal median section of the apple, each of these ten vascular bundles is seen to 

 give rise to branches, which in turn branch again and so on, mostly towards the outside, although 

 there are several branches on the inside (Fig. 94). From each of these ten strands, just as they are 

 leaving the stalk, branches are given off to the outer and inner face of the seed-cavity, so that the 

 seeds are well supplied. The main strands, however, are associated with the " flesh," and the 

 diverging branches towards the outside do not divide much until they approach the skin, where 

 they form a perfect network (Figs. 86, 90). This vascular net envelopes the flesh about one-quarter 

 of an inch or less from the surface, and this wonderful and hitherto unsuspected structure not only 

 unites the entire system of vessels, but gives rise to the innumerable plume-like branches which 

 reach even to the skin (Fig. 91). These arise from the boundaries of each mesh of the net, and they 

 divide and subdivide in such a luxuriant manner that the ultimate branchlets interlace and 

 intertwine so as to form a seemingly continuous layer of conducting tissue beneath the skin. They 

 penetrate the cells immediately beneath the epidermis (Fig. 85), which are particularly rich in 

 chlorophyll, and take an active part in the nutrition of the growing and swelling fruit. In the 

 longitudinal section, the main strands are seen to come together again just at the " eye," where 

 they pass out into the calyx, corolla, and stamens, so that the entire flower, including the carpels, 

 is fully supplied with vascular bundles. 



The green colour of the bundles, seen in a cross section of the apple, is due to chlorophyll. 

 This is made evident when a longitudinal section of the bundle is made. The chloroplasts or 

 chlorophyll-granules are seen not only in the cells intermixed with the vessels, but also in cells 

 outside of them. They are ellipsoid in shape, and vary in size, but generally average 3-4£ microns 

 in length. 



VASCULAR BUNDLES AS A WHOLE. 



In order to get a connected view of the vascular system as a whole, it is necessary to 

 remove the soft parts, so that the strands of conducting tissue may be isolated. In the case of 

 the apple, the bundles were separated out by means of a dilute solution of potassium hydrate. 

 After macerating in this for a week, the soft pulpy material was readily detached, leaving the 

 strands intact. It was laid out in water, and, by means of brush and needle, all the soft parts 

 were removed, leaving only the ten strands, with their ramifications, as photographed. (Fig. 88 ) 



We are all familiar with the Egyptian Loofah, or Towel Gourd, used like a sponge for the 

 bath, and which is just the fibro-vascular bundles of the fruit of Luffa cegyptiaca. It is probably 

 prepared by retting or steeping in water, to get rid of the soft parts. The " skeleton " of the 

 apple leaf, formed by exposure to the weather, is also a familiar object (Fig. 130). In the case 

 of the pear, it was found that after immersion for five days in ordinary tap water, the skin 

 could be easily peeled off, and the flesh removed, so that the vascular system, forming a 

 complete outline of the fruit, stood out distinctly, as in Fig. 83. The quince is a little 

 tougher, and required longer immersion in water, but the vascular network is similar, with the 

 innumerable projecting, plume-like branchlets. 



FUNCTIONS OF THE BUNDLES. 

 The functions of the bundles are twofold. There is a vascular portion, to convey the 

 nutritive fluid to each part where wanted, and a fibrous portion, to strengthen the delicate cells 

 and prevent collapse. It is necessary to understand how the growing apple is nourished, in order 



