n .EQUATORIAL VEGETATION 263 



their delicate foliage. Where a large surface of ground is 

 thus covered the effect of walking over it is most peculiar. 

 At each step the plants for some distance round suddenly 

 droop, as if struck with paralysis, and a broad track of 

 prostrate herbage, several feet wide, is distinctly marked out 

 by the different colour of the closed leaflets. The explana- 

 tion of this phenomenon given by botanists is not very 

 satisfactory ; l while the purpose or use of the peculiarity is 

 still more mysterious, seeing that out of more than two 

 hundred species belonging to this same genus Mimosa, only 

 a small number are sensitive in any remarkable degree, and 

 in the whole vegetable kingdom there are but few other 

 plants which possess more than the rudiments of a similar 

 property. The true sensitive plants are all low-growing herbs 

 or shrubs with delicate foliage, which might possibly be liable 

 to destruction by herbivorous animals, a fate which they may 

 perhaps escape by their singular power of suddenly collapsing 

 before the jaws opened to devour them. The fact that one 

 species has been naturalised as a weed over so wide an area 

 in the tropics, seems to show that it possesses some ad- 

 vantage over the generality of tropical weeds. It is, however, 

 curious that, as the most sensitive species of Mimosa are 

 somewhat prickly, so easy and common a mode of protec- 

 tion as the development of stronger spines should here 

 have failed ; and that its place should be supplied by so 

 singular a power as that of simulating death in a manner 

 which suggests the possession of both sensation and volun- 

 tary motion. 



Comparative Scarcity of Flowers 



It is a very general opinion among inhabitants of our 

 temperate climes that amid the luxuriant vegetation of the 

 tropics there must be a grand display of floral beauty, and 

 this idea is supported by the number of large and showy 

 flowers cultivated in our hothouses. The fact is, however, 

 that in proportion as the general vegetation becomes more 

 luxuriant, flowers form a less and less prominent feature ; 

 and this rule applies not only to the tropics but to the tem- 



1 See Nature, vol. xvL p. 349, where the German botanist Pfeffer's theory 

 is given. 



