FRUITS AND SEEDS 195 



berry-like fruits, whether true or false — e.g., grapes, 

 gooseberries, hips, etc. — are to be regarded as dehiscent, 

 the fruit being broken open by birds. The biological 

 classification of fruits and seeds depends upon the agents 

 of their dispersal : 



1. Wind-Dispersed Fruits and Seeds — (a) Fruits.— These 

 are invariably one-seeded — e.g., achenes and mericarps. 

 They are either light or small, or, if large, they are 

 smooth, so that they may easily be rolled along over 

 the surface of the grQund. Some are specially provided 

 with hairs or wings. The achene of the dandelion 

 (Fig. 82) has a hairy pappus, derived from the calyx-,- 

 which acts as a kind of parachute. In the thistle the 

 pappus is sessile (Fig. 103). The achene of clematis 

 (Fig. 104) is provided with a long feathered awn, derived 

 from the style ; while the mericarps of the stork's-bill 

 (Erodium) and the pelargoniums have curved awns 



Fio. 103. — Achene (Cypskla) ot Fio. 104. — ^Achene of Clematis 



Thistle. with Peatheby Style. 



furnished with a fan of spreading hairs. Winged achenes 

 are found in the samaras of the ash (Fig. 83) and- the 

 mericarps of the sycamore and maple (Fig. 94). 



(5) Seeds. — These are borne in capsules, which only 

 dehisce when the weather is warm and dry, or when it is 

 windy. The dehiscence is caused by the desiccation of 

 the walls or parts of the walls. In most cases the seeds 

 are very small and light. In the poppy the capsules are 

 shaken by the wind, and the seeds jerked out through 

 the valves. The dust-like seeds of the orchids are the 

 smallest known. In pods the seeds are often large — 

 e.g., peas and beans — ^but they are smooth and round, 

 and over an even surface they may be blown along by 

 the wind some distance from the parent plant. In a 

 few cases the seeds are provided with special mechanisms 

 for wind-dispersal ; in the willowherb, willow, and poplar, 

 they are feathered, like little thistle-fruits ; in the pine 

 they are winged. 



