478 BOTANY 



Carnivorous Plants 



A small number of the higher plants are known, which have de- 

 veloped special means of obtaining nitrogen from organic bodies. 

 These are the "carnivorous" plants, like the Sundew (Drosera) 

 and Pitcher-plants (Sarracenia, Nepenthes, etc.). These are usually 

 aquatic or bog-plants, which grow where the soil nitrogen is inad- 

 equate, and the traps formed by their leaves, for capturing insects 

 and other small animals, are, with little question, adaptations for 

 supplying the deficiency of nitrogen. 



Ash-elements 



In addition to the carbon, hydrogen, oxygen, and nitrogen, which 

 constitute the greater part of the substance of the plant, there are 

 present in the ash left after the plant is burned, an amount of incom- 

 bustible matter, ranging from 1.5 per cent to as much as 30 per cent 

 of the dry weight. Some of these ash-elements, like iron and potas- 

 sium, are essential, others, like silica and iodine, are not necessarily 

 present. 



METABOLISM 



The various products of chemosynthetic and photosynthetic activ- 

 ity of the plant undergo many further changes, both destructive 

 and constructive, before they finally become part of the living pro- 

 toplasm. It is these changes which constitute Metabolism, a subject 

 much too extensive to be taken up here in detail. 



Proteids 



First in importance in the active life of the plant are the various 

 nitrogen compounds, which contribute to the growth of the proto- 

 plasm. Of these the Proteids are the most abundant, and of first 

 importance. Asparagin and other soluble nitrogenous substances 

 (Amides) are often, but not always, present, and may be an important 

 reserve-food, but are never constituent parts of the protoplast; while 

 the living protoplast is probably composed largely of a mixture of 

 proteids. Proteids also occur as reserve-food in seeds, tubers, etc. 



The Carbohydrates 



The carbohydrates are all, primarily, the product of photosyn- 

 thesis, and are the principal source of energy to the plant, as well as 

 the source of organic food. Starch, sugar, cellulose, are the common- 



