93 



the light it turns green, and it is the starch-forming corpuscles 

 which, though normally colourless, can and do become green 

 under the action of the light. The correspondence between the 

 chlorophyll corpuscles and these colourless corpuscles which 

 exist in the internal reservoirs is then a very close one. 



Each starch-forming corpuscle consists of a small portion of 

 differentiated protoplasm, which varies in shape according to 

 the plant examined ; in many plants they are rod-shaped in 

 form ; — in the potato tuber, however, they are circular. They 

 are especially abundant in the immediate neighbourhood of the 

 nuclei of the cells ; thus if the cells of a section of a tuber of the 

 potato immersed in alcohol be examined, a number of those 

 protoplasmic circular bodies will usually be found surrounding 

 each nucleus. The starch grain in its earliest stage of develop- 

 ment projects from each of these as a little hump or protuber- 

 ance on^one side of the corpuscle, which, when treated with 

 iodine, turns a blue colour, showing that it is starch that is 

 present. As the starch grain grows rapidly, in later days we 

 find that it has increased enormously in size, while the corpuscle 

 is then almost undistinguishable and is soon lost sight of. The 

 starch grain of itself cannot grow, it is only able to do this in 

 consequence of certain processes of change taking place in these 

 corpuscles. Directly the starch grain becomes free from its 

 starch-forming corpuscle all further growth ceases, for it can 

 only grow so long as its connection with the starch-forming 

 corpuscle remains unbroken. 



Since the sugar solution is thus deposited, a demand for a 

 further supply will be created, which has to be supplied. But 

 in the spring, when growth is active, the starch in the sub- 

 terranean reservoirs — roots, tubers, rhizomes, &c. — becomes at 

 once reconverted by the action of a ferment into solution of 

 sugar, to fit it for being more easily carried, and in this form 

 it passes upwards by diffusion through the parenchyma cells 

 towards the leaves. The movement of this solution of sugar 

 is now known as the "slow movement of fluids in plants" 



That the starch is reconverted into sugar is well known. 

 Starch grains have been observed in various stages of disap- 



