FRUITS AND SEEDS 233 



The stimulus which the process of- fertilisation imparts to 

 the ovule, and which results in the development of the seed, is 

 also transmitted to the tissues of the ovary wall. This is best 

 seen in the case of the flowers of pears and apples, where we 

 can distinguish a very few days after the flowering, with a con- 

 siderable degree of certainty, which of the flowers have been 

 fertilised. In these the flowering stalk is much more turgid 

 and begins to thicken very soon. 



With the progressive development of the seed changes also 

 take place in the carpels which bear them, so that the green 

 ovary becomes changed into the ripe fruit. The wall of the 

 ovary often becomes differentiated into three layers : the 

 outermost layer {epicarp), a median one (mesocarp), and an 

 inner one (endocarp). If they all three become hard and dry, 

 the fruit is termed a dry fruit (hazel-nut, pod of pea, or 

 capsules of lily and poppy). If, however, one or more layers 

 become fleshy, then we speak of succulent fruits (gooseberry, 

 fruit of the melon, drupe of cherry and plum). The cherry- 

 stone is not the' seed of the cherry, but the hard inner 

 portion of the ovarian wall, and encloses the actual seed. 

 It is^ .iflso .important to know that the fruit of the pear and 

 apple is what is termed a false fruit or pseudo-carp, in the 

 formation of which the axis of the flower or receptacle plays a 

 part. In the case of the strawberry, too, we really eat the 

 fleshy receptacle upon which the actual fruits are borne as 

 numerous small nutlets. In the case of the raspberry and 

 blackberry, however, we are dealing with a number of true 

 succulent fruits which are crowded together on a common 

 receptacle. In the case of the pine-apple, mulberry, and fig, 

 the entire inflorescence becomes sweet and succulent. The 

 spiny coat surrounding the nuts .of the Spanish chestnut is not 

 the ovary wall, but an involucre or cupule made up of four 

 bracts, and of the same nature as the cup of the acorn. 



§ 45. How can the formation of the fruit be influenced by 

 different methods of cultivation? 



At the end of the last chapter we dealt with the mode of 

 formation of fruits and of fruit-like structures (pseudo-carps), 



