STRUCTURE.] BEHAVIOUR WITH WATER. 117 



hole, and the entire grain then looks swollen like a very 

 thick-skinned bag. By degrees the cleft becomes less distinct, 

 but it is evident that the pasty masses thus produced, always 

 are traceable into a grain ; and if a thin starch paste is mixed 

 with water, and viewed under a microscope with a little iodine, 

 the single swollen grains will be visible, whilst the additional 

 water is not stained blue. I tried for a whole day to separate 

 the boiled grain without success, but I think I may venture 

 to conclude from my experiments, that starch can absorb a 

 large (but limited) quantity of water, and can consequently 

 swell to a great size, but that it never actually dissolves in 

 either cold or hot water. 



Lastly, I may mention the behaviour of starch with cold 

 water. If some starch is rubbed down with twice its volume 

 of water for half an hour, a viscid, ropy, stiff paste will be 

 obtained. Under a microscope a large part of the grains 

 appears variously crushed, torn, divided, and partly pounded 

 into small flocks, the inner (watery) layers are especially 

 pressed out as it seems through the action of the rubbing and 

 their combination with more water, presenting a flaky or 

 granulated entangled mass, which may be stained blue by 

 iodine, whilst the surrounding water remains quite colourless. 

 All these experiments were made with purchased (impure) 

 Potato starch, and always gave the same results. In every 

 experiment iodine was employed, and I never observed the 

 remotest indication of any part in the grains of starch which 

 refused to be coloured by iodine. 



From these observations it must be evident, that without 

 the combined use of a microscope and chemical re-agents, 

 an exact knowledge of starch cannot be hoped for. 



In a growing potato, the starch gradually becomes dissolved, 

 so that often after three months scarcely a trace of starch can 

 be found. The grain of starch preserves its solidity to the last 

 moment, being gradually acted upon from without inwards, 

 and in such a way that, the ends of its principal axis making 

 most resistance, the grain by degrees assumes the appearance 

 of an uneven rod. 



B. On the occurrence of Starch in Plants, and its various 

 forms. The useful treatise of Fritsche (Poggend. Ann. 



