310 STUDIES, SCIENTIFIC AND SOCIAL 



present the conditions which elsewhere are said to pro- 

 duce 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 have more 

 spiny plants than Chili, 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 Gleditschia 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, notwithstanding its moist insular climate, we have 

 an Olea and an Osmanthus with holly-like prickly leaves ; 

 while the prickly Berheris Darwinii is found in the damp 

 atmosphere of the Straits of Magellan. 



Equally opposed to the theory of aridity as the efficient 

 cause of 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 Astro- 

 caryum are thus armed, as is also the beautiful Guilielma 

 speciosa, the Peach palm, whose fruit is large and edible. 

 It is a suggestive circumstance that, with the exception 

 of palms, few large trees are spiny, and when they are 

 so, as in the case of the Gleditschia, the spines are most 

 abundant on the trunk and on the younger branches. In 



