THE FRUIT AND SEED-DISPERSAL 321 



and nourishment are afforded during development. But they are 

 still better secured in inferior ovaries ; for in these the ovules are 

 surrounded also by the massive tissue of the receptacle, while they 

 are brought nearer to the source of vascular supply by their deeply 

 sunken position. The protection becomes more effective as the 

 maturing of the gynoecium proceeds, for its tissues frequently become 

 more bulky and succulent. But still more is this so in others which 

 harden with age. Extreme cases are seen in nuts or stone-fruits, 

 where the woody tissues of the carpel reinforce, or sometimes mechani- 

 cally replace the seed-coats. Since the seed with its nutritive store 

 offers attractions to animals as food, the biological importance of 

 such strong mechanical protection should be duly recognised. 



But the biological fact which has dominated the evolution of the 

 fruit, as regards its development after fertilisation, more than any 

 other is the need for the dispersal of the seeds. The greater their 

 number the greater is the need for it. Sooner or later each seed 

 should have the opportunity of germination. This is carried out 

 with the best prospect of success where each is isolated from its 

 neighbours. Moreover, a wide dispersal leads to the spread of the 

 species, and thus helps it in that competition for room in an over-, 

 crowded world which has been called the Struggle for Existence. 

 The size of the individual seed is an important factor in the problem 

 of dispersal. Clearly, the larger the seed the better is the chance of 

 successful establishment of the young plant on germination ; for the 

 larger the store it carries with it the larger the vegetative system it 

 will be able to form before it has to depend on its own resources. 

 But the larger the seed the less easily will it be transferred from point 

 to point. There are thus two conflicting factors of success. In the 

 course of evolution plants have severally struck their own balance 

 between these opposing factors, and the variety of fruit-construction 

 shows in what different ways the problem may be solved. The success 

 of each may be measured by the survival, numbers, and spread of 

 those plants which have adopted them. These are the underlying 

 conditions which should be kept in mind in studying the structure 

 of the fruit, and its relation to seed-dispersal. 



It is probable that a primitive type of gynoecium was apocarpous, containing 

 a number of ovules. Such a carpel is seen in the pod of a Pea, or in the follicle 

 of Caltha or Aquilegia. Along several lines of Descent comparison suggests 

 that there has been a reduction in the number of ovules to a single one. This 

 is illustrated in the Ranunculaceae. The Helleboreae have follicles and are 

 probably a central type {e.g. Helleborns, Aconitum, Caltha, Fig. 240). In 



B.B. X 



