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 ground. 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 
Fie. 103.—AcHENE (CYPSELA) OF Fic. 104.—AcHENE oF CLEMATIS 
THISTLE. WITH FEATHERY 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). 
(b) 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. 
