126 THE PHYSIOLOGY OF STOMATA. 



observed in the blue, though photosynthesis may occur to some extent. 

 The quantitative differences noted hold for blue as well as for red light. 



(2) The accumulation of starch in the guard-cells in the darkness and, 

 it seems highly probable, in C0 2 -free air also, is contingent upon the presence 

 of starch or related substances in the subjacent portions of the chlorenchyma. 

 Following the complete removal of all carbohydrates from the leaf when sub- 

 jected to suitable conditions, there ensues a gradual reduction of the starch 

 content of the stomata. This loss is irregular as regards different stomata, 

 those being more favorably placed as, e. g., near the vascular tissues, showing 

 a less rapid loss of starch. This starvation of the leaf, and the consequent 

 starvation of the stomata, has been shown to occur in prolonged darkness, 

 in prolonged exposure to blue light, and we may infer also, in the continued 

 absence of carbon dioxid, under the conditions, namely, which prevent any 

 accumulation of starch (blue light), or prevent photosynthesis entirely, in the 

 cells of the chlorenchyma. 



When a plant in a thoroughly starved condition is exposed to diffused light, 

 the formation of starch appears to occur less rapidly in the stomata than 

 in the chlorenchyma. 



That the guard-cells derive their starch chiefly from the underlying tissues 

 rather than through the photosynthetic activity of their own plastids is a 

 view strengthened by the observation that young stomata which are not yet 

 functional, and frequently long before they are exposed to light, are found 

 to be richly supplied with starch. The very young though completely 

 formed stomata which are to be found near the bases of the leaves still 

 inclosed within the terminal bud of Agave contain starch, while none of 

 this may be detected in the leaf chlorenchyma. At this time there is no 

 trace of chlorophyll either in the chlorenchyma or stomata. Even at an 

 early period in the development of the leaf, therefore, the difference between 

 the chlorenchyma and stoma plastids becomes apparent, and other evidence 

 shows that this difference continues to obtain through the whole life of the 

 stoma. 



Starch has been shown to occur in mature stomata which have never been 

 exposed to the light, by Sachs, Leitgeb, and MacDougal, and I have observed 

 this to be true of other plants than those examined by these authors. It 

 occurs also in stomata devoid of chlorophyll, according to Leitgeb (1888), 

 and when this substance is very meager in amount, by myself. 



(3) The movements of stomata take place under conditions which prevent 

 photosynthesis, as in the absence of carbon dioxid; and in blue light (c/. 

 Kohl, 1895), when, if it takes place, it is reduced to a small amount. There is 

 evidence also that movements occur in prolonged darkness (Francis Darwin, 

 1898), and the open condition has been observed in total etiolation experi- 

 ments in many plants (MacDougal). There is, in addition, evidence that in 



