CHAPTER XXVI 



THE STRUCTURES AND PROCESSES CONCERNED IN FRUIT 

 FORMATION 



The entire flower may be regarded as a specialized branch, consisting 

 of a central axis to which are attached several whorls or sets of organs 

 that bear a certain resemblance to leaves. The two outer or lower 

 whorls, the calyx and corolla, take no direct part in reproduction and 

 are spoken of as non-essential organs, though after fertilization the 

 calyx may undergo considerable differentiation and form a considerable 

 part of the mature fruit. As stated before, the stamens bear the male 

 gametes. In the higher plants, exclusive of the gymnosperms, the female 

 gametes are developed inside an enclosed structure, the ovary. This 

 last may consist of a single carpel (or modified leaf, to follow the concep- 

 tion of one school of botanists) or of several that are more or less com- 

 pletely united. In the latter case the ovary and the fruit which develops 

 from it, may be several-loculed. That portion of the central axis of the 

 flower to which the several sets of floral organs are attached is the recep- 

 tacle or torus. 



A fruit may be defined as a ripened ovary together with whatever 

 may be intimately attached to it at maturity. If it consists of a ripened 

 ovary only, as in the peach or tomato, it is a simple fruit; if it includes 

 additional structures it is spoken of as an accessory fruit. Sometimes 

 the accessory structure may be the torus, as in the apple; sometimes 

 the torus and the calyx, as in the cranberry and sometimes a part of 

 the peduncle or pedicel, as in some varieties of the pear. The developing 

 ovaries of certain fruits grow together and give rise (1) to aggregate 

 fruits, if they all belonged to the same flower, as in the raspberry, or 

 (2) to multiple fruits if they belonged to different flowers, as in the 

 mulberry. In the latter the mature fruit includes ovarian, toral and 

 stem tissues. Not infrequently the ovarian tissues constitute only a 

 small part of the mature fruit and as a rule it is the accessory tissues 

 (when they are present) in which the pomologist is mainly interested, 

 for they are likely to constitute most of its edible portion. However, 

 it is the ovary with its enclosed ovules on which fruit formation 

 depends; consequently a discussion of fruit setting and fruit formation 

 must start with the ovary and its ovules. 



The Ovule. — The ovule arises as a protuberance from the inner wall 

 of the ovary. The particular points, lines or surfaces from which it 



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