LECTURE VI 

 PROTECTIVE ADAPTATIONS IN PLANTS 



Protection against large aniinals — Poisons — Ethereal oils— Spines and thorns — 

 Sharp and stinging-hairs — Felt-hairs — Position of the thorns : buckthorn — Tragaeanth 

 shrub— Prigana scrub— Alpine shrubs — Protection against small enemies— Chemical 

 substances —Mechanical protective arrangements — Raphides — Conclusion. 



We have seen in how many different ways animals are able to 

 adapt themselves to the conditions of life, both protectively and 

 aggressively ; how they approximate in their colour to that of their 

 surroundings so that they harmonize with it ; how they copy lifeless 

 objects, or parts of plants, leaves, or twigs, or even mimic, in form 

 and colour, other animals which are in some way protected. When 

 we consider that by far the greater number of species find protection 

 in some degree through their colouring, and often through their foi-m, 

 and when, at the same time, we remember how different this colouring 

 is in nearly related species, and even within the same species (dimor- 

 phism), we can scarcely avoid the impression that the forms of life 

 are made of a plastic material, which, like the sculptor's clay, can 

 be kneaded at will into almost any desired form. 



This impression is corroborated when we turn our attention to 

 plants, and consider the different ways in which they are able to 

 protect themselves from the attacks of animals. 



That plants stand in need of some protection is obvious enough, 

 since their leaves and other green parts contain much nourishment, 

 and an endless army of animals, large and small, depends upon these 

 alone for sustenance. Indeed, the existence of animals depends 

 altogether on the occurrence of plants, for carnivorous and saprophytic 

 animals could only arise after vegetarian forms had been already in 

 existence. But if the green parts of the plants were left defenceless 

 at the mercy of the multitude of herbivorous animals, it would not be 

 long before they were exterminated from the face of the earth, for the 

 animals would devour unsparingly whatever was within their reach, 

 and, as their increase does not depend on their ratio of elimination 

 alone, but also on their fertility, and on their rapidity of multiplica- 

 tion, they would go on increasing in numbers at the expense of the 



