ECOLOGICAL 195 



rather leathery, and the seed adheres to it. In such cases 

 fruit and seed are practically identical; what is sown is 

 the fruit. 



(4) Among the soft fruits there are two main types — the stone- 



fruits, like cherries and plums, and the true berries, like 

 gooseberries and grapes. In stone-fruits, the hard part or 

 "stone" is the third and innermost layer of the fruit, the 

 endocarp, and the pulp is the middle layer or mesocarp. 

 Inside the stone the familiar kernel is of course the seed. In 

 true berries, on the other hand, the hard part is the wall of 

 the seed; and the pulp of the fruit often contains several 

 seeds. It is interesting, though not relevant to ecology, to 

 think out some of the difficult fruits; thus it seems that a 

 coco-nut is a stone-fruit in which the pulp is represented 

 by the fibrous layer used in making mats; and that the 

 walnut is a stone-fruit, for outside the familiar stone or 

 nut there lies the firm, fleshy middle part corresponding to 

 the juicy part of a peach. 



(5) Berries are soft fruits without a hard endocarp (innermost 



fruit- wall), but with a hard coat round each of the seeds, 

 which are embedded in the pulp. Even ecologically it is of 

 some importance to understand clearly that the seed of a 

 cherry, let us say, is inside the hard stone of the fruit, 

 whereas the hard bodies inside a grape are the seeds, each 

 with a very strong envelope. A gooseberry is a typical 

 berry, but there are some difficult forms, such as oranges, 

 with hard seeds embedded in the centre of a pulp composed 

 of much enlarged juicy cells. Even more difficult is the date, 

 where the seed inside the fleshy pulp has its own nutrient 

 tissue (endosperm), though of almost bony hardness. 



Modes of Dispersal. — ^There are five main ways in which seeds 

 (or fruits in certain cases) are scattered: — (i) by the wind, (2) by 

 water currents, (3) by explosive dehiscence, (4) by attachment to 

 animals, and (5) by being swallowed by animals. 



(i) Dispersal by means of the wind is well illustrated by dandelion- 

 down and thistledown and the like, where the nutlet fruit, con- 

 taining a seed, is wafted by the wind, often for great distances. 

 The world-wide representation of the groundsel genus, Senecio, is 

 in part associated with the effectiveness of the fruit's parachuting, 

 due to the development of a tuft of hairs (pappus) on the top of the 

 nutlet or cypsela. The fruit of the common Clematis or Traveller's 

 Joy is a nutlet with a feathery plume on its tip, the hoary appear- 

 ance of the crowded plumes giving origin to another of this favourite 

 plant's many names — Old Man's Beard. When many fruits are 

 simultaneously set free by the breeze, the plumes are often entangled 



