196 BRITISH PLANTS 
2. Explosive Fruits and Seeds.—In explosive fruits, the 
walls, when ripe, suddenly explode, and eject the seeds 
with some force into the air. In the balsam, touch-me- 
not (Impatiens Noli-me-tangere), and wood-sorrel, the walls — 
are somewhat succulent, and explode suddenly through 
the tension set up in warm, dry weather by the rapid 
loss of water from them. The geraniums afford an 
excellent example of explosive schizocarps (see p. 190). 
In the squirting cucumber, a berry-like fruit becomes so 
turgid that it bursts, shooting out a watery pulpy mass 
in which the seeds are embedded. In the wood-sorrel 
(Oxalis Acetosella) the seeds are not only expelled from the 
capsule, but out of their own arils ; in this case the seeds 
themselves may be regarded as explosive. The pods of 
the gorse and the siliquas of the cuckoo-flower (Carda- 
mine pratensis) pop in dry weather. In the Viola the 
seeds are shot away one after another from the open 
capsule, by the drying and contraction of the margins of 
the dehisced sections (Fig. 105). 
3. Fruits and Seeds distributed by Birds.—These are 
generally succulent, in which case some provision is 
always made to prevent the seeds from being eaten. In 
berries the seeds are hard and indigestible ; in drupes the 
seeds are enclosed in a stone, and this is always dropped. 
Some seeds ejected from capsules are covered with a 
succulent coat—the aril ; this is eaten by birds, and the 
kernel within rejected—e.g., spindle-tree, fcetid iris, 
wood-sorrel. Among the conifers the seeds of the yew 
and juniper have succulent integuments ; in the yew it 
is an aril; in the juniper fused bracts. 
Seeds of all kinds are eaten by birds, and many are 
destroyed in this way, especially the grains of cereals. 
Some of them, however, may, by some accident, escape 
complete destruction and get distributed. 
Darwin points out that birds may be the means of 
dispersing seeds in another way. If the ground is damp, 
they pick up a good many seeds on their dirty feet. In 
one case he found that eighty seeds germinated from a 
small pad of soil which he took from the foot of a bird. 
4. Animal-Dispersed Fruits and Seeds.—(a) Seeds eaten 
by animals—e.g., nuts and oily seeds—are enclosed in 
tough skins or hard shells which have to be torn or broken 
open before the food can be obtained. Many are de- 
