MIMETIC RESEMBLANCES AMONG PLANTS. 



327 



MIMETIC RESEMBLANCES AMONG PLANTS. 

 By Rev. Prof. G. Henslow, M.A., V.M.H., c<;c. 



[.July 2, 1901.] 



Inthoductiox.^ — Mimetism, as it has been called, is a well-recognised 

 feature among animals. One animal, as a butterfly, may superficially re- 

 semble another in form and colour, but have no real or close affinity with 

 it. Others, as the Kalima Inachis of India, when its wings are closed, 

 look like dead leaves. Caterpillars on Willows, S:c., resemble bits of 

 broken twigs. Sec. Again, in Australia, which had originally only Mar- 

 supials among mammals, Nature has evolved out of that one family 

 genera which elsewhere form separate groups of mammals, such as the 

 carnivora, insectivora, rodents, &c. Even a mouse finds its exact 

 counterpart in a pouched little animal of precisely the same form 

 (Antechiniis muiutissinius). Lastly, all animals of whatever kind that 

 frequent the deserts have acquired a similar tawny colour to that of the 

 sand ; and Arctic animals are white when they are surrounded by snow. 

 But illustrations are too numerous to mention, and can be taken from 

 all groups of the animal kingdom. 



In the vegetable kingdom, resemblances between plants of no affinity 

 are extremely common, and the obvious reason is that they li\"e under 

 the same or similar climatal conditions. In the animal kingdom the 

 cases of the resemblances to each other are equally numerous ; but 

 the general inference applies to all, viz. that the mimetic resemblances 

 are presumably the result of such animals living under identically the 

 same conditions and so becoming influenced by their environments. 

 Mimetism among plants is best seen in those living under surroundings 

 of some pronounced character, and will be well illustrated in the following 

 examples : — 



Desert Floras. — Certain types of plants are very characteristic of hot. 

 dry, sandy, or rocky localities, where rain falls but seldom, and water 

 must be stored up against the dry season lasting for some nine months 

 or so. Under these circumstances stems or leaves become thick and 

 fleshy, and provision is made in the anatomical structure of the siu-face 

 to resist undue loss of water by transpiration. 



As remarkable examples take the members of the Cactus family of 

 Mexico, which have thick, massive, angular stems, the leaves being 

 wanting, but represented by spines. Precisely similar stems occur in the 

 Euphorbias of the Soudan, &c., and again in the Stapelias of South Africa, 

 and other plants of other orders. These coincidences are obviously due 

 to the plants responding to the external influences of their environment 

 and assuming similarly adaptive structures. 



Another feature is the spinescent type. Branches and leaves become 

 represented by spines in many different plants in deserts; just as the 

 Gorse and Needle-furze (two distinct genera) are spiny on our own 

 heaths, as well as the Rest-harrow by the roadsides. This spinescence is 



