i8o NATURAL SCIENCE. Sept.. 



to the whole plant ; succulent foliage ; special protection of the buds ; 

 enormous development of roots; abundance of bulbs and tubers; 

 together with thickness of bark and various protective coatings to 

 stems and leaves. Now many of these peculiarities are present in 

 the flora of the Brazilian Campos — as well described in the memoir 

 of Eug. Warming on Lagoa Santa — which is referred to by 

 Mr. Henslow as corresponding in many respects with that of other 

 arid regions. Yet the author of this memoir expressly states that 

 "spiny plants are very rare" (p. 463). Again, the plants of the 

 Galapagos present similar indications of aridity — shrubs with minute 

 and almost invisible leaves, for example — yet, except the cacti, which 

 may be of American origin, none of the endemic species are spiny. 

 So, also, the rich Sandwich Island flora contains hardly a single 

 endemic spiny plant ; and I am informed by the Rev. R. P. Murray, 

 who is well acquainted with the botany of the Canaries, that spiny 

 plants are exceedingly rare in those islands, though much of the surface, 

 owing to the porous volcanic rock and the long periods of drought, 

 presents the conditions which elsewhere are said to produce spines. 



Now without denying that — other conditions being equal — aridity 

 may favour and moisture may check the growth of spines, there is 

 another and altogether different set of conditions which seem more 

 directly connected with their abundance or rarity. This is, the 

 presence or absence of herbivorous mammals, against whose ravages 

 spines are a protection. The most destructive of these animals are 

 camels, goats, and antelopes, and it is where these are indigenous — 

 in Arabia, North-east and South Africa, and Central Asia, that thorny 

 shrubs and trees are especially abundant. Again, few countries ha\-e 

 more spiny plants than Chih, where the camel-like vicugnas and 

 alpacas, as well as large rodents, are very destructive. But the 

 country is not especially arid, and the remarkable Puyas, whose 

 leaves are armed with excessively sharp recurved spines, inhabit the 

 subalpine regions where rain and mist prevail. In our own moist 

 islands we have a full proportion of prickly plants, and the same may 

 be said of North America, where the Glcditschia or Honey Locust 

 has the young branches, and in old trees the trunk, armed with 

 groups of very strong and sharp spines. So also in Japan, notwith- 

 standing its moist insular climate, we have an Olea and an Osman- 

 thus with holly-like prickly leaves ; while the prickly Berbens 

 Darwinii is found in the damp atmosphere of the Straits of Magellan. 

 Equally opposed to the theory of aridity as the efficient cause ot 

 spines is their abundance on palms growing in the hottest and 

 moistest regions of the globe. In many Amazonian species the stem 

 is thickly set with long and very sharp spines pointing downwards, 

 and thus forming a complete protection against monkeys and other 

 arboreal fruit-eating mammals. Many species of Bactris and 

 Astrocavynm are thus armed, as is also the beautiful Guiliehna spcciosa,. 

 the Peach palm, whose fruit is large and edible. It is a suggestive 



