STOMATA AND THE SPECTRUM. 1 09 



swathing the bell-jars on one side with cloths kept wet by irrigation, the 

 rapid evaporation having a sufficiently cooling effect. In but few instances 

 did the temperature get beyond normal limits, and then not sufficiently high 

 to vitiate the results of the experiments. The objections which might be 

 raised to the use of cuttings are disposed of by the uniformity of results 

 obtained by both methods employed. The high humidity of the interior, 

 which may be objected to, may, I believe, be disregarded, since there is no 

 evidence that this condition materially modifies the processes within the guard- 

 cells; while its influence upon the size of the stomatal openings is exerted 

 only indirectly, as in the case of wilted plants. In the CO 2 -free air experi- 

 ments the composition of the air within the bell- jars was controlled by means 

 of caustic potash and lime or baryta water. 



The data obtained include not only the size of the stomatal openings, but 

 the conditions of the starch and oil content of the guard-cells and the starch 

 content of the near-by chlorenchyma. Observations of the chlorenchyma 

 adjacent to the stomata have been made in every case, since it offers a con- 

 venient and very necessary standard by which to judge the condition of the 

 starch content of the guard-cell. The estimation of the amount of starch 

 present in the plastids is purely a matter of judgment, based upon constant 

 experience. The stomata were examined after proper treatment with potas- 

 sium iodide-iodine by means of a Leitz i /i6 oil immersion, which was used 

 also in making the photomicrographs. For clearing, which is not always 

 necessary but preferable for photography, glycerine or chloral hydrate was 

 used. In order to swell the starch grains I had recourse to boiling, or 

 chloral hydrate or potash. The latter two reagents, however, as is well 

 known, disorganize the starch, so that their use is not to be depended upon, 

 especially when very small granules are to be examined. Experience taught 

 me that even boiling was of little value, as one then has to depend upon a 

 more or less vague color effect merely, while in the unaltered material the 

 size of the granules of starch is quite apparent after some practice in observa- 

 tion. Material in the fresh condition and after treatment with absolute 

 alcohol has in all cases been used, the latter being better, inasmuch as the 

 iodine reaction is not then masked by the presence of the chlorophyll in the 

 adjacent cells. The photographs were, for the greater part, made from 

 specimens of epidermis mounted in temporary fashion in absolute alcohol or 

 in glycerine-iodine solution, the former for the size of the stomatal apertures 

 and the latter for the starch content. In all cases epidermis of the same col- 

 lection was examined at least twice, and usually three times, at considerable 

 intervals of time, in some cases after the lapse of a year. In this way a 

 valuable check on one's personal judgment may be obtained. 



