202 



ELEMENTARY BIOLOGY 



of the plant where they do not interfere with the vital activities. 

 There are many classes of such waste compounds. 



I. Among the most common waste substances found in 

 plants are various pigments. These are familiar to us in the 

 autumnal colorings of leaves, in the bright colors of many 

 flowers and fruits, and in the pigments of woods and roots. 

 The red of the radish, of the rose, and of the maple leaf, 



the yellow of the buttercup, of the 

 pumpkin, and of the carrot, and the 

 blue of the pansy and of the huckle- 

 berry, all are examples of the waste 

 products that are deposited in out-of- 

 the-way cells (Fig. 75). 



2, The attractive odors of many flow- 

 ers, preserved for us in perfumes and 

 essences, and the flavors of the many 

 spices are due to essential oils de- 

 posited in out-of-the-way cells of plants. 

 They are found in the flower, the leaf, 

 the fruit, the bark, the wood, and even 

 in the root. 



3 . Tannins are chemical compounds 

 related to tannic acid which have the 

 property of forming hard, insoluble 

 compounds with proteins. They are 

 commonly found in the bark of trees, but 



may also occur in other parts of the plant — often in unripe fruits. 



4. The acids that we find in fruits especially, although they 

 are present in other plant organs, are derived from substances 

 diftused out of live cells. Alkaloids (see p. 74) and other 

 poisonous substances found in plants, and the gums and resins, 

 are also waste products. 



5 . The excess of mineral matter absorbed from the soil is 

 separated out of the live cells by being deposited in cell walls 

 or by being precipitated as insoluble compounds in certain ol 



Fig. 75. Pigment bodies in 

 plant cells 



Most of the pigments found in 

 the cells of plants are probably 

 in the nature of waste products. 

 Some pigments occur in solu- 

 tion ; others are found attached 

 to protein particles, forming 

 definite colored granules 



