''DEFENCE, NOT DEFIANCE^ 157 



for existence;" without such a "struggle," however, 

 the organic world would never have attained a much 

 higher rank than that of scarcely differentiated 

 particles of protoplasm. As observation is extended, 

 every characteristic of plants will be found to bear 

 reference to its present or its past wellbeing and 

 protection. Some of the characters are still retained 

 in their structures, although no longer necessary or 

 requisite, just as we keep up certain fictions in law 

 and etiquette — " survivalisms " of once important 

 functions. 



The trifoliate leaves of the Clovers, Oxalis, and 

 a few other plants, close at night ; and there can 

 be little doubt that by doing so they present a less 

 surface to the late frosts which often linger on to the 

 season when the leaves are green and in active 

 work. The leaves of many Australian trees have 

 acquired the trick of turning the edges of their 

 leaves upwards, for the contrary purpose of exposing 

 as little surface as they can to the dry and intense 

 heat of the sun. To this end their leaf-stalks give a 

 half-twist, and so continue to present the edge only 

 to the sun as it travels across the heavens. The 

 stomata or carbon -feeding mouths of their leaves, 

 instead of being placed on one side (generally the 

 lower) of the leaf, in the leaves of these Australian 

 shadeless trees, are arranged on both sides. By 

 thus exposing a limited, indeed a minimum, surface 

 of leaf to the sun, such trees prevent the evapora- 



