DEFENSIVE EQtnPMENT OF PLANTS 137 



Dry fruits, like capsules, are not wortK 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. 



(6) 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- 



-a 



Fio. 47. — AcoEN WITH Fio. 48. — Ediblb Chestntit, with Three 



Habd Cupule (a). Nttts (a) enct.osbd in Spiny Ctrpui,E (6). 



ditions. This hardiness is brought aboiit 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 

 germiaation, water is absorbed and the cells become 

 turgid. The xeroph3^ic characters of the seed are 

 primarily a protection against natural perUs — drought, 

 cold, etc. — ^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 among which they lie. It is another case of 



