9 2 



current of sugar solution will then be carried from the leaves 

 to the seeds, or downwards to the base of the stem to some 

 depository or reservoir, (root, rhizome, tuber, or bulb), because 

 it is being there deposited bodily as starch (sometimes, however, 

 it continues to exist in the form of sugar — e.g., in the onion), 

 and stored up either for use by the plant in the succeeding 

 'year, or for the development of the embryo, for in both of 

 these cases there will be a demand for it which must be supplied. 

 Starch, then, travels down from the leaves in a soluble form, 

 through the parenchymatous cells to the cells of the tubers and 

 other subterranean reservoirs, which are unable to form it for 

 themselves, since they possess no chlorophyll, but only store it 

 up by re-depositing it in the bodily form of starch in consequence 

 of deriving a supply of sugar solution from the leaves. The 

 parenchyma cells of the plant, in which the sugar solution 

 passes, have always a very acid reaction to test paper ; and it 

 may be, as I have said, that the sugar is temporarily in the 

 form of an acid, to enable it to be more easily transferred from 

 one part of the plant to another. The transference of carbo- 

 hydrate material does not, moreover, take place in one single 

 stage only — that is, by starch being converted into sugar at the 

 leaves, and this again re-converted into starch at the reservoirs; 

 but it is interrupted or halts at certain periods on the way 

 before it reaches its final destination, and the sugar solution is 

 thrown down here and there, in the insoluble form of starch, in 

 cells which are not reservoirs for starch : this latter at a subse- 

 quent period is re-dissolved. 



The change of starch from the soluble form of glucose to the 

 insoluble form in the reservoirs does not take place promiscu- 

 ously in all the protoplasm of the cells of the tubers, &c, as was 

 at one time believed to be the case, but is confined to certain 

 special portions of it, forming bodies known as starch-forming 

 corpuscles. These have been most specially studied by A. F. 

 W. Schimper, in the tubers of the potato, and also in various 

 roots and rhizomes* If a piece of a potato tuber be exposed to 



• " Researches upon the Development of Starch Grains," Botanhcht Zeitung, ;88o, 

 No. 5», translated in Stuart. Jour. Micros. Set., New Series, lxxxii., April, 1881. 



