ba 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 ;' 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. xvi. p. 849, where the German botanist Pfeffer’s theory 
is given. 
