CONCLUSIONS. 129 



which conclusion the evidence of the present contribution has been arraigned, 

 we are forced to believe that the chlorophyll of the guard-cells is of relatively 

 minor importance. The admission that the chlorophyll is active, as in the chlo- 

 renchyma cell, involves the further one that during the early part of the day, 

 when opening takes place, photosynthesis and the dissolution of the stored 

 starch within the chloroplasts occur at the same time in the same plastids. 

 We must therefore favor the explanation that the products of photosynthesis, 

 (relatively small in amount as compared with the amount available from the 

 starch derived by translocation, and already in the plastids) do not immedi- 

 ately take the form of starch ; but that when the maximum opening has passed 

 they may, along with the other osmotic substances, then be formed into 

 starch, except, of course, a part which may have escaped by diffusion. The 

 ability of the chloroplastid to secrete starch if supplied with the appropriate 

 materials (Meyer, 1883) suggests the view that, as regards their functions, 

 the plastids of the guard-cell and of the chlorenchyma-cell differ quantitatively 

 in that while both are capable of both photosynthesis and secretion, their 

 normal activities in these two directions are in inverse relation. The guard- 

 cell plastid is normally and chiefly a leucoplast, while the chlorophyll-cell 

 plastid is, in like manner, a photosynthetic organ. The relative importance 

 of the photosynthesis in the stoma is small enough so that the movements 

 of the stomata are affected but little by its cessation, as must in all proba- 

 bility intervene under conditions which are known to make photosynthesis 

 impossible. 



This view makes it possible to harmonize results such as those of Kohl 

 on the one hand and those of Leitgeb and Francis Darwin on the other. If 

 turgor-raising substances are present in sufficient amounts the stoma must 

 open; and while these will be normally present, even if the appropriate con- 

 ditions for photosynthesis are not supplied, yet, if photosynthesis may occur, 

 the osmotic turgor-raising substances may thereby be additionally formed. 

 Whether, however, the amount formed by photosynthesis is sufficient alone 

 to effect the opening in the blue light to the extent indicated by the experi- 

 ments of Kohl and those recorded by myself is not yet to be answered. 



In the case of stomata with a large amount of chlorophyll, if we may assume 

 that the effectiveness of a plastid is related to the amount of chlorophyll pres- 

 ent in it (which is said by Pfeffer not to be of necessity the case), it may be 

 argued that the products of photosynthesis would be sufficient to bring about 



conditions generally unfavorable to the remaining tissues of the leaf. Thus in Galtonia, 

 after an interval surprisingly long, namely, one month, during which time the underlying 

 tissues had become discolored and impregnated by the mycelia of fungi, the stomata 

 remained living and were shown by him to be capable of photosynthesis. According to 

 Molisch the "concentration of the cell sap, the size of the cells, capillarity, and the specific 

 constitution of the plasma" all probably contribute to this result. The results of both 

 these authors afford general support to the present contention, but are open to various 

 interpretations, none of which are as yet proven to be true. 



