694 THK FIRRO-VASrULAU SYSTKM OF TIIK QUINCK, 



increasing size and enlargement of the carpels and the flesh. If 

 we start with the net-work in the fruit just formed, as in Fig. 10, 

 the pressure exerted by the continuous growth of the flesh and eon- 

 ducting tissue combined, will not merely cause the net to stretch, 

 but the conducting tissue will be added to. Just as the cells of the 

 flesh enlarge, so will the conducting tissue which conveys the nutri- 

 tive material necessary for their expansion, increase, and there will 

 be a mutual accommodation between tlie growing flesh and the con- 

 ducting tissue, which conveys the nourishment. 



One cannot fail to be struck with the analogy, in a broad sense, 

 between tlie blood-capillaries in the human body and the vascular 

 or capillary net in the flesh of a pome, both serving to regulate the 

 flow of nutriment, and equalise its distribution. 



Professor J. S. Macdonald, in his presidential address before the 

 Section of Physiology at the meeting of the British Association for 

 the Advancement of Science(1911), referred to the blood-capil- 

 laries as follows: "They are no more and no less than blood-tissue. 

 In its early days, this blood-tissue, or if you will, this capillary 

 network, is pushed into each portion of the body by pressure due 

 to its growth. In its later stage, the tissues surrounding it, which 

 form the muscular coat of the heart, and the walls of the blood- 

 vessels, are arranged into an external mechanical system providing 

 a new pressure, which still further tends to push the blood-tissue 

 into every available space." Without straining analogy too far, we 

 may say that the capillary net-work in the pome is acted on by 

 pressure, due not only to its own growth, but by the surrounding 

 enlarging tissue; and in this way, it meets the increasing demands 

 made upon it under ordinary conditions, as tlie fruit grows larger 

 and larger. 

 Comparison of the Vascular System in Apple, Pear, and Quince. 



There is a general resemblance in that of each of the three 

 fruits, but there are differences in detail, largely dependent upon 

 differences in the shape and texture of the respective fruits. There 

 are the same number of primary bundles in each, and the general 

 distribution is the same, but owing to the shape of the fruit in the 

 pear, the vascular bundles run together for a greater distance 



