CONCLUSIONS. 131 



Kohl 's conclusion is then 



Da nun an diesen Stellen des Spectrums auch die Turgorsteigerung in den Schliesszellen, 

 welche zur Oeffnung des Spaltes fiihrt, eintritt, folgere ich, dass es auch in erster Linie die 

 in den Chloroplasten der Schliesszellen die Production der Starke sowohl als auch die der 

 Starke-umsetzenden Fermente in den Schliesszellen der Stomata bewirken (p. 4). 



The case as presented by Kohl is suggestive, but the explanation, plausible 

 as it appears, is not beyond criticism. Starch being "always present," it 

 is difficult to see why the supposedly present amylolytic ferments are not 

 stimulated to activity by all the light except that in the region of the 

 violet (Green, loc. cit.), since in the present state of our knowledge we may 

 not confine the fermentative activity solely to the red and the blue. Indeed, 

 even the presence of an appropriate ferment in the guard-cells has not yet 

 been demonstrated, although there is every reason to believe it to be pres- 

 ent Moreover, Kohl's theory appears to lead to the view that the amy- 

 lolytic ferment is active at the time of photosynthesis, but does not explain 

 how both processes may take place at once. The actual disappearance 

 of starch during the early part of the day, as observed by myself, indicates, 

 however, that a ferment is indeed active; and, as I have said above, if 

 photosynthesis takes place, the products must in all probability not assume 

 the form of starch until later, thus adding them to the osmotic substances 

 obtained from the stored starch. That by photosynthesis alone the starch 

 of the guard-cell is obtained, we may not believe, in view of the facts presented 

 by Leitgeb (1888), Francis Darwin, and myself, relating to the accumulation 

 of starch in the stomata in the absence of carbon dioxid and under other con- 

 ditions which do not result in the formation or accumulation of starch in the 

 chlorenchyma, and to the opening of the stomata under these conditions, 

 with the concurrent disappearance of starch leading, except in darkness, to 

 as full an amplitude of movement as under normal conditions. To these 

 must be added the reformation of starch in the latter part of the day, even 

 when light is excluded (Verbena). The objection that, in experiments in 

 which the carbon dioxid is excluded, there may be a sufficient amount avail- 

 able for the use of the stomata as a product of respiration, may be met in 

 part by the observation that no trace of photosynthesis has been noted to 

 occur in nearby chlorenchyma cells, to which the excreted gas has access 

 equally with, if not even more directly than, the stomata. 



Kohl's suggestion that there is present in the guard-cell an amylolytic 

 ferment is of especial interest, but the mere fact that in a solution of diastase 

 the stomata open can hardly be said to prove anything in this regard, since 

 diastase is highly non-diffusive, and, moreover, many stomata open in water. 



As already said, the presence of a ferment has not demonstrated, and my own 

 attempts in this direction have failed. Leitgeb 's observations on Galtonia 



