194 Reserve Material of Plants. 



We may consider all reserve material as occurring in two 

 forms, the liquid and the solid. Of the former we have examples 

 in the oils, sugars, inulin and allied compounds, although the two 

 latter may also be obtained in a solid form under certain special 

 conditions of treatment. Of the latter we have familiar examples 

 in the various kinds of starch which, however, is most probably also 

 a liquid at certain times, as when in process of transfer from one 

 organ to another. We should also enumerate, among the solid 

 forms of reserve material, those peculiar forms which protoplasm 

 assumes when passing into the resting state, such as are to be 

 found in the crystalloids, aleurone, etc., or in other words, in the 

 so-called protein compounds of seeds. 



It is not the purpose of this paper to discuss all, or even a 

 large portion of these compounds, since the subject is altogether 

 too large to permit of proper treatment within such brief limits, 

 and I shall therefore confine my remarks to that one form of most 

 frequent and conspicious occurrence, starch, since what is true of 

 this in its distribution and relation to pathological conditions, is 

 also true in a very large measure of the other forms of reserve 

 material ; and, moreover, it is in the distribution of this in health 

 and disease with which our investigations have been chiefly con- 

 cerned. * 



The leaves are the special organs of digestion for the plant, 

 and to them we may consider this function wholly confined ; 

 except in cases where there is a green bark, as in all herbaceous 

 plants and the young shoots of woody plants, or where true leaves 

 are absent, and their function is assumed by other parts of the 

 plant, as in the cacti. The products of digestion are in general 

 the same in either case, as, also, must be their final distribution 

 and use, so that what is true of the leaves in their relation to the 

 digestive function must also be true of other green parts. The 

 essential features of the digestive process, as we observe it in leaves, 

 are the decomposition of C0 2 and H 2 with recombination of 

 their constituent elements, giving rise to starch as a solid product 

 to be utilized in nutrition, while free O is liberated into the sur- 

 rounding air whence the C0 2 was derived. This action may be 

 regarded as continuing during the entire vegetative period, so 

 long as chlorophyll is present and sunlight has free access to the 

 leaves, and, therefore, under otherwise uniform conditions, sub- 



