272 THE BIOLOGY OF THE SEASONS 



illustration some of the fruits that are popularly and 

 erroneously called " nuts." Why is a Brazil-nut not a 

 nut ? Because it is a seed one of many from a large box. 

 Why is a pea-nut not a nut ? Because it is a pod. Why 

 is a walnut not a nut ? Because it is the stone of a drupe. 

 Why is a horse-chestnut not a nut ? Because the fruit 

 is really a capsule with big seeds. Why is a cocoa-nut not 

 a nut ? Because it is the stone of a large drupe with a 

 leathery epicarp and a fibrous mesocarp. The hazel 

 has a typical nut with a sheath of succulent bracts at 

 the base; the beech has three-sided nuts with woody 

 external bracts ; the acorn is a nut with an extra scaly 

 cupule. 



Towards an understanding of fruits, a few suggestions 

 may be offered. In the case of succulent fruits, we have to 

 remember that the green plant is a sugar-factory, that it is 

 an extremely anabolic organism with an income greatly 

 n excess of its expenditure, that it makes very much 

 more sugar than it needs, that some of this surplus over- 

 flows in the nectaries of the flowers, and that after the 

 nectaries close up the surplus may be drafted into the fruit. 

 Having got this elementary but fundamental fact clear, 

 we may go on to the secondary interpretation that juicy 

 fruits are well adapted for seed-scattering by fruit-eating 

 birds, and that plants with juicy fruits will therefore, in 

 certain conditions, prevail. 



Again, in regard to fruits of the capsule type, which 

 liberate the seeds by splitting, either gently or explosively, 

 we have to remember that the sides of the box are usually 

 the carpels that is to say, leaves modified for the production 

 of seeds. These carpels, like other leaves, are organs of a 

 limited length of life ; they are likely to die and wither, 

 and crack and shrivel, and fall off like other leaves. And, 

 again, it is this primary fact that should come first, and 



