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n .EQUATORIAL VEGETATION 263their delicate foliage. Where a large surface of ground isthus covered the effect of walking over it is most peculiar.At each step the plants for some distance round suddenlydroop, as if struck with paralysis, and a broad track ofprostrate herbage, several feet wide, is distinctly marked outby the different colour of the closed leaflets. The explanationof this phenomenon given by botanists is not verysatisfactory ;while the purpose or use of the peculiarity islstill more mysterious, seeing that out of more than twohundred species belonging to this same genus Mimosa, onlya small number are sensitive in any remarkable degree, andin the whole vegetable kingdom there are but few otherplants which possess more than the rudiments of a similarproperty. The true sensitive plants are all low-growing herbsor shrubs with delicate foliage, which might possibly be liableto destruction by herbivorous animals, a fate which they mayperhaps escape by their singular power of suddenly collapsingbefore the jaws opened to devour them. The fact that onespecies has been naturalised as a weed over so wide an areain the tropics, seems to show that it possesses some advantageover the generality of tropical weeds. It is, however,curious that, as the most sensitive species of Mimosa aresomewhat prickly, so easy and common a mode of protectionas the development of stronger spines should herehave failed ;and that its place should be supplied by sosingular a power as that of simulating death in a mannerwhich suggests the possession of both sensation and voluntarymotion.Comparative Scarcity of FlowersIt is a very general opinion among inhabitants of ourtemperate climes that amid the luxuriant vegetation of thetropics there must be a grand display of floral beauty, andthis idea is supported by the number of large and showyflowers cultivated in our hothouses. The fact is, however,that in proportion as the general vegetation becomes moreluxuriant, 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 theoryis given.