64 PLANT PHYSIOLOGY 



the rate of removal in twenty-four hours, there will be an 

 increasing excess of food in the chlorophyll-containing tis- 

 sues. If this continues for a number of days, the leaves 

 will become filled with accumulated starch, etc., will become 

 abnormally heavy, and by their unusual plumpness, differ- 

 ence in color, etc., will give evidence of their morbid condi- 

 tion: Such "fatness" of leaves is sometimes found in nature, 

 more frequently, however, in cultivation. The cure is easy : 

 shading the plants will reduce the rate of food manufacture 

 and permit the nightly emptying of the daily filled cells. 



When food is deposited in indiffusible form in any cell, it 

 must be dissolved before it can be removed. Water is in- 

 variably the vehicle of food substances in the plant as in the 

 animal body, and the foods are carried from cell to cell only 

 in solution. Starch grains, deposited either in the chloro- 

 pla.stids, in which the carbohydrate is formed, or in the 

 adjacent cytoplasm, must be converted into sugar and 

 dissolved before they can be removed. In the chloro- 

 phyll-containing cells which manufacture food in the light 

 and accumulate the manufactured product in the form of 

 starch, diastase or some similar starch-converting enzym" 

 must be present in the green tissues of leaves, and in other 

 chlorophyll-containing parts. To demonstrate its presence, 

 however evident its effects may be, is diflicult, because of the 

 very small amount required to do the work in the time 

 allowed the plant. To convert a large amount of starch 

 quickly into sugar, a comparatively large amount of dias- 

 tase is needed. If the time be longer, less diastase will do 

 the same work. Its converting power is astonishingly great 

 — 10,000 times its own weight of starch.* The removal of 

 food goes on constantly. Its manufacture is only periodic. 

 A small amount of diastase secreted by the cell will therefore 

 accomplish, in the twenty-four hours, the removal of all the 

 starch normally deposited in the cell as the result of photosyn- 

 thetic activity. That diastase is formed in small quantities 

 in green leaves is indicated by the investigations of Vines, f 



* Schleichert, F. Das diastatleche Ferment der Pflanzen. Halle, 1893. 

 t Vines, S. H. On the presence of a diastatic ferment in green leaves. 

 sAnnals of Botany, V., 1891. 



