STARCH. 



39 



absorption of carbonic dioxide, the evolution of oxygen, and 

 the formation of starch, which first manifests itself in the 

 form of minute solid particles — starch grains — ^within the 

 chlorophyll corpuscles. The formation of starch grains is a 

 rapid process under favourable conditions, especially in the 

 lower plants, appearing after five minutes' exposure to bright 

 sunlight in Spirogyra, a minute fresh-water alga, and after 

 about two hours in the Screw moss, Funaria hygrometrica. 



Fig. 8. — ( X 540). Starch grains from a potato tuber, A, a simple grain show- 

 ing the lines of stratification and the nucleus or hilum at c. C and D, 

 compound grains, formed by the development of new hila in an 

 ordinary grain, each hilum being surrounded by its own layers. (From 

 Strasburger.) 



Starch is very widely distributed in all plants except 

 fungi, in which group it is entirely absent. It appears under 

 the form of minute colourless grains, varying in shape, but 

 constant in each species ; usually oval, sometimes spherical 

 or lenticular, and marked with concentric or eccentric lines 



