RESPIRATION. 179 



In consequence of having such a store of material, 

 tubers can grow in the dark as long as the material holds 

 out, but will not, of course, produce green leaves. 



Besides starch, oil is a common form of reserve material, 

 particularly in seeds. Sugar, also, is found; as, for 

 example, in the Sugar-Beet. 



310. Parasites and saprophytes, which are as a rule 

 without chlorophyll, do not assimilate, but obtain their 

 nourishment from the stores of other plants or from 

 decomposing organic matter. 



311. The so-called carnivorous plants, such as the 

 Bladder-wort and the Pitcher-plant, obtain a portion of 

 their nitrogen by entrapping insects and other small 

 animal organisms, and absorbing them as they decompose. 

 Some such plants appear to cover their prey with an acid 

 secretion, and to go through a digestive process not 

 altogether unlike that performed by animals. 



312. Respiration. Plants, like animals, are continu- 

 ally inhaling oxygen, and the presence of this gas is 

 essential to their existence. The oxygen so inhaled is 

 combined with carbon to form carbon dioxide, and this in 

 the day-time is at once decomposed and the carbon 

 assimilated. The absorption of oxygen and its subsequent 

 combination with organic matters in the plant is accom- 

 panied by evolution of heat, a fact well illustrated in the 

 process of malting, where damp barley is heaped together. 

 As soon as the grain begins to sprout, oxygen is rapidly 

 absorbed, and a very decided rise of temperature takes 

 place. The starch of the grain is oxidised and converted 

 into sugar, and the growth is then stopped by rapid drying. 

 The sugar, on fermenting, produces alcohol. 



