116 



way it must bo conceded that the opportunity for the action of a ferment in the leaf 

 is extremely limited. 1 Such action requires time and much more favoable conditions 

 than can be found in the living leaf. In any case if sugar be formed from starch in 

 either of the ways indicated it could not be sucrose. 



In fact the reducing sugar which is found in plants is seldom starch sugar, i. e., mal- 

 tose or dextrose. This appears to be a fact which the vegetable physiologists have- 

 entirely ignored. The sugars of plants which reduce an alkaline copper solution 

 are either derived from sucrose by inversion, or more probable are of independent 

 formation. If they were derived from starch they would show dextro- if from su- 

 crose, laevo-gy ration. In point of fact they often show neither, as I long ago pointed 

 out, when, in view of this optical inactivity, I proposed for them the name of anop- 

 tose. When they do show rotation, however, it is left-handed. 



It seems to me that there is one fact that the physiologists forget, viz, that starch 

 is not always insoluble. In my examinations of sorghum juices I have never failed to 

 find soluble starch when I looked for it. 3 The existence of bodies when first formed 

 in the soluble state, which when once made solid become insoluble, is not unknown. 

 Certain forms of silica are illustrations of this. It seems much more reasonable to sup- 

 pose that in the case of the sorghum, for instance, the starch which appears in the seed 

 is partly transferred directly from the soluble nascent state to the seat of its final depo- 

 sition. This, indeed, is hardly a theory in the light of the fact mentioned above 

 that the sap of the plant always contains soluble starch. 



It is far more simple to suppose that the sucrose which we find in sorghum is pro- 

 duced directly by the decomposition of protoplasm in presence of carbonic acid, pro- 

 voked by the katalytic action of the chlorophyll cell. At any rate there is no sort of 

 evidence that it is ever made from starch, and no physiologist has ever invented any 

 hypothetical saccharoplast to account for such a transformation. 



This subject of the origin of sucrose is of great interest ; but I have not yet finished 

 my experimental studies of it, and so will not pursue it further at present. 



The question now arises is the sucrose of sorghum a plastic material, reserve mate- 

 rial, or waste ? In respect of plastic material it is sufficient to call attention to the 

 fact that the development of sucrose does not begin in the plant until it is far on the 

 road to maturity. To this it may be objected that its accumulation does not begin 

 until this period, and that what is formed earlier in its history is a really plastic ma- 

 terial used in the development of other tissues. Had I time I might show, I think, 

 conclusively, that the presence of the sucrose as a plastic material is not probable. 

 Is itr a reserve material ? The sucrose which is deposited in the seeds of plants, in 

 tubers like the sugar-beet, and in sugar-cane, doubtless is a true reserve material, 

 and by its decomposition helps the growth of the succeeding plant. But the sucrose 

 in sorghum seems to have no such function. It can in no way aid the incipient 

 growth of the next plant, for that plant grows from a seed. As far as any use in the 

 economy of the plant is concerned, it appears to be absolutely worthless. It is true 

 that in the case of " suckering," the sucrose in the cane may suffer loss, but "sucker- 

 ing " is not always a natural growth; it is adventitious and is always detrimental to 

 the proper maturity of a plant. 



It seems, therefore, that the sucrose in sorghum is purely a waste material as 

 much so as an alkaloid or a resin. 



In the cases where sucrose is a true reserve material, as in seeds, in tubers, and in 

 sugar-cane, we find there is no tendency for it to disappear until the needs of the new 

 plant require it. The sucrose remains, for instance, unchanged in the sugar-beet 

 until the new growth begins. The same is true in a higher degree of the sucrose in 

 seeds. The fact, therefore, that in sorghum all traces of sucrose may disappear in a 

 few days shows that its office is radically different. 



1 The ferment which acts on the starch has been studied by Brasse and Schimper 

 (Bied. Centralblatt, vol. 14, p. 169, vol. 15, pp. 310 and 473). It is called amijlase, 



2 That is a body in solution which gives a blue color with iodine. 



