608 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



HOW FRUITS ARE MADE. 

 By Rev. Prof. G. Henslow, M.A., V.M.H., &q. 



[Lecture to the Students at the Society's Gardens, July 9, 1902.] 



The Effects of Pollination and Fertilisation. — In considering 

 how fruits are made, it is very obvious to all that in most cases, if no 

 fertilisation has taken place by means of the pollen, the fruit falls pre- 

 maturely without " setting " ; but it is equally true that in some cases the 

 ovary may swell and grow into an edible fruit without any seeds being 

 present at all. Thus, we have grocers' currants and sultana raisins, both 

 these being forms of seedless grapes ; there are also seedless oranges, 

 bananas, cucumbers, and pines. 



This may result from either of two causes. In the case of grapes and 

 oranges, it would seem that the effect of pollination is to introduce a 

 stimulus to the growth and development of the ovary only. This 

 frequently occurs in artificial hybridisation. Thus a large fruit is often 

 formed by crossing Orchids, promising great things to the hybridiser, but 

 it may finally be found to contain nothing but hairs and no seeds at all. 



The usual effect of pollination is, of course, the fertilisation of the 

 ovules, which then become seeds, each containing an embryo. Simul- 

 taneously w T ith this, the ovary enlarges and acquires the characters of the 

 fruit, peculiar to its kind. 



Further, in many fruits the axis or floral receptacle takes part in 

 forming the fruit, in the popular sense of the word. The enlargement 

 and changes undergone in so doing are primarily the indirect effects of 

 pollination. 



We thus find the floral receptacle of the Strawberry can develop into 

 an enormous mass of succulent tissue whereon are situated the true fruits 

 in the form of seed-like bodies called " achenes." As another instance, 

 the "hip" of the Rose is a hollow " receptacular tube " containing numerous 

 and separate achenes. 



In some instances pollination affects other accessory parts, as the 

 calyx of the Mulberry. Of every little flower of the cluster which makes 

 the "fruits," the four sepals become fleshy and purple, constituting the 

 edible part, the true fruit or pistil in the middle being dry and seed-like. 



Such have been called " pseudocarps," or "false fruits," since the 

 edible part has nothing to do with the pistil, out of which the fruits are 

 made. 



As other examples, the cup of the acorn, of the Beech-mast and of the 

 Spanish chestnut, as well as the leafy cupule of the Hazel and Hornbeam, 

 are " after-growths," which would not have occurred had the seeds not 

 baen formed within the fruit by fertilisation. 



So that, when we think of the importance of pollination for the ferti- 

 lisation of the ovules, we must remember that everything else results 

 indirectly from the stimulus set up in consequence of pollination, with or 

 without fertilisation. 



