DEFENSIVE EQUIPMENT OF PLANTS — 137 
Dry fruits, like capsules, are not worth eating. Other 
fruits escape destruction by concealing or disguising their 
presence. Protective mimicry is common among animals 
and insects, but it is only observed here and there in the 
vegetable world. Thus, some ripe fruits appear like dead 
twigs—e.g., wallflower ; others are like small stones— 
e.g., smooth and dull-coloured achenes. Sometimes, how- 
ever, mimicry may serve to attract attention. Thus, the 
achenes of the marigold resemble caterpillars. Birds 
pick them up and carry them some distance before they 
find out their mistake. 
(b) Seeds.—On p. 108 we pointed out that the seed was 
the xerophytic structure par excellence, with a wonderful 
tenacity of life, and with an extraordinary capacity for 
withstanding long periods of the most unfavourable con- 
Fic. 47.— AcoRN WITH Fic. 48.—EpDIBLE CHESTNUT, WITH THREE 
Harb CUPULE (a). Nuts (a4) ENCLOSED IN SPINY CUPULE (0). 
ditions. This hardiness is brought about by the with- 
drawal of water, so that the seed becomes partially 
desiccated, and the embryo is reduced to a state of sus- 
pended animation. Activity is only resumed when, on 
germination, water is absorbed and the cells become 
turgid. The xerophytic characters of the seed are 
primarily a protection against natural perils—drought, 
cold, ete.—but the withdrawal of water renders them hard, 
and therefore impossible as food to swarms of living 
creatures. Dry structures are not subject to disease, 
since fungi and bacteria only flourish where moisture is 
abundant. Apart from this, however, seeds show special 
protective devices. Many are small and dull in colour, 
so that they cannot easily be distinguished from the soil 
particles ameng which they lie. It is another case of 
