132 THE PHYSIOLOGY OF STOMATA. 



candicans in the isolated moribund stomata of which he observed the dis- 

 appearance of starch and oil, and my own on Verbena, in the stomata of which 

 there is a daily reduction of starch,* leads irresistibly to the conclusion that 

 there is a protoplasmic activity to which this is due, and the natural assump- 

 tion is that the mechanism involved is a ferment. Wortmann championed 

 the view that the dissolution of starch in the cell is not affected by a ferment, 

 but by the direct action of the protoplasm (1890); but the trend of research 

 has unceasingly favored the belief that there is an intermediate mechanism, 

 the ferment. f 



Here, however, we tread on very debatable ground, and, in the case of the 

 stoma, almost purely theoretical. J. R. Green (1899, p. 74), in his generally 

 excellent summary of our knowledge of enzymes, points out in regard to 

 stomata merely the teleological aspect of the question, and does not attempt 

 to explain why the "diastase" in the stomata should act differently from the 

 diastase of the chlorenchyma. As already pointed out, Kohl supposes an 

 enzyme to be present whose activity, in the light of Green's later studies 

 (1894) on the influence of light on diastase, is in some obscure way connected 

 with photosynthesis. It seems that it will serve the best purpose in this con- 

 nection to point out as clearly as may be the facts which must be considered 

 in any attempt to formulate a theory of enzymatic activity in the stoma. 

 The most fundamental difference to be noted as between leaf diastase and of 

 the stoma is in the normal relation to light. Leaf diastase does its work ordi- 

 narily in the dark. J If stoma diastase did so, there would be a disappearance 

 of the starch in the night. This, however, is not the case. This inhibition 

 of the process of starch dissolution can not be due to the presence of sugars 

 or other osmotic substances (Wortmann) since the stomata are almost or 

 quite closed, and in this condition these substances can not be present in quan- 

 tities greater than those in the adjacent epidermal cells (Kohl, 1895). What- 

 ever the amount, it is not great enough to inhibit the action of the supposed 

 diastase at dawn, until which hour the starch content remains unaffected. 

 This leads to the next consideration, namely, that the secretion of the ferment 

 or its activity is stimulated by light. If the relation of the stoma ferment 

 to the rays of different refrangibility be the same as that of ordinary diastase 

 (Green, loc. cit.), we may suppose that the early morning light would be stimu- 



*The behavior of the oil in the stomata of this plant need not be considered in this 

 connection. 



fG. Krabbe (1890) believed that diastase originates in the cell that uses it, as it can not 

 pass, unless chemically changed and rechanged, from one cell to another. This certainly 

 seems to be the case, since the starch in dead chlorenchyma cells does not appear to be 

 digested even at points in close contiguity to adjacent living cells. This is true also of the 

 stoma, in which, when one of the guard-cells is dead, this may be found richly loaded with 

 starch, though the other guard-cell may contain no starch at all in consequence of digestive 

 activity (plate 14, fig. 5). From this observation we may conclude that the special ferment 

 of the guard-cell, if it exists, originates in that cell, and may not escape from it. 

 J Though light does not inhibit its activity (Brown & Morris, 1893, p. 624). 



