BOTANICAL RESEARCH — MACDOUGAL. 12$ 



cells (described in the previous report), and confirmatory results have been 

 obtained. In addition to the earlier experiments on the effect of darkness 

 and air deprived of carbon dioxid, others have been done on the effect of the 

 different parts of the spectrum, from which the following briefly summarized 

 conclusions have been derived. 



In all parts of the spectrum the movements of stomata are the same 

 qualitatively, such quantitative differences as have been observed being easily 

 and properly explained on the grounds of general starvation. This is 

 apparent from the fact that in the blue-violet end of the spectrum the ampli- 

 tude of movement grows gradually less after the third day, as compared with 

 the amplitude of movement in the red end of the spectrum. In view of the 

 persistence of starch in the stomata under both these conditions, and in view 

 of other contributory evidence, it appears clear that the food content of the 

 guard cells is derived, in large part at least, from the adjacent chlorenchyma, 

 and upon the continual starvation of this latter, the effect is to make it impos- 

 sible for the stomata at length to obtain material from which energy may be 

 obtained. Little if any movement occurs in the darkness, and a persistent 

 exposure to this condition results in the starvation of the guard cells, but not 

 for three or more days. In general the data obtained are in confirmation of 

 the truth of the theory first suggested by Kohl, that the phenomena of 

 stomatal action are explicable only by an understanding of the behavior of 

 the enzymes resident in the guard cells, for which theory, however. Kohl 

 failed to offer convincing evidence. 



Experiments have also been done to test the theory of induced rhythm 

 as applied to stomatal action. Evidence had been previously obtained in 

 1905 that such rhythm occurs in transpiration. Francis Darwin had also 

 held this view for stomatal action, but experiments of the same general 

 character as those of Darwin done on the Virginia creeper (Ampelopsis 

 quinqnefolia) are distinctly inconclusive if not inimical to Darwin's view. 

 Also on the matter of stomatal action during wilting, during which Darwin 

 holds there occurs a preliminary opening, the data as recent!}^ obtained are 

 unequivocal, showing that a continual closure, concomitant with, and due to, 

 wilting, occurs. 



Topography of Chlorophyll-masses, by Dr. W. A. Cannon. — The highly 

 adaptive relations sustained by desert plants to light and humidity as evi- 

 denced by the aspect and structure of their shoots necessitates concomitant 

 modifications of the disposition of the tissues bearing chlorophyll, which is 

 usually present in large quantity in xerophytic forms. When the species 

 bears only the rudimentary leaves, or none at all, the chlorophyll in twigs, 

 branches, and stem is particularly well marked. Certain desert trees, as 

 Parkinsonia microphylla and the other species of this genus, owe their 

 characteristic color almost wholly to the chlorophyll present in the cortex of 



