64 PIGMENTS 



Carotin is present in considerable quantity in the root of the 

 Carrot, to which it imparts the orange colour. 



A considerable number of plants are still used as the source 

 of dyes ; thus the dried stigmata of Crocus sat km s yield saffron, 

 and the rhizome of Citrctima longa (tropical Asia) the yellow dye 

 turmeric. 



It is doubtful whether any of the substances dealt with in 

 this chapter are produced for their intrinsic utility to the plant. 

 But it is quite possible that the poisonous alkaloids, the astringent 

 tannins, or the pungent resins may render the plants containing 

 them distasteful to herbivorous animals, and so prove indirectly 

 Ijeneficial. Similarly the antiseptic character of resin may well 

 be of service in protecting a wound over which it has congealed. 

 Tyndall showed that the vapour of ethereal oils tends to diminish 

 the passage of heat through air, so that their common occurrence 

 in plants of dry situations may be a means of checking evapora- 

 tion by retarding the heating effect of sunshine. It may be, 

 however, that some of the substances here referred to constitute 

 a means of storage of food-material, and this applies especially 

 to some of the tannins which seem to have the structure of 

 glucosides. 



