224 TROPICAL NATURE, AND OTHER ESSAYS. 



ophrydis, of South Africa, as strikingly resembling an 

 orchid. This may be a means of attracting insects to 

 fertilize the flower in the absence of sufficient nectar or 

 other attraction in the flower itself ; and the supposition 

 is rendered more probable by this being the only species 

 of the genus Ajuga in South Africa. Many other cases 

 of resemblances between very distinct plants have been 

 noticed — as that of some Euphorbias to Cacti ; but these 

 very rarely inhabit the same country or locality, and it 

 has not been proved that there is in any of these cases 

 the amount of inter-relation between the species which is 

 the essential feature of the protective mimicry " that 

 occurs in the animal world. 



The diflerent colours exhibited by the foliage of plants 

 and the changes it undergoes during growth and decay, 

 appear to be due to the general laws already sketched 

 out, and to have little if any relation to the special 

 requirements of each species. But flowers and fruits 

 exhibit definite and well-pronounced tints, often varying 

 from species to species, and more or less clearly related 

 to the habits and functions of the plant. With the few 

 exceptions already pointed out, these may be generally 

 classed as attractive colours. 



Attractive Colours of Fruits. — The seeds of plants 

 require to be dispersed, so as to reach places favourable 

 for germination and growth. Some are very minute, 

 and are carried abroad by the wind ; or they are violently 

 expelled and scattered by the bursting of the containing 

 capsules. Others are downy or winged, and are carried 

 long distances by the gentlest breeze ; or they are hooked 

 and stick to the fur of animals. But there is a large 

 class of seeds which cannot be dispersed in either of these 



