14 BEHAVIOR OF STOMATA. 



The question of the time of starting and ending a series was also 

 of importance. It was especially desirable that no gap should occur 

 between the first and last strip collected. If a series began with the 

 stomata closed and ended with them closed, the course of events 

 leading to the opening and final closing could be followed throughout, 

 but if it began with them closed and ended with them open, the time 

 of closure would be in doubt, and the series left without a definite 

 ending. At first it was thought that the best time to start a series 

 would be just before dawn, as the stomata would have all night to 

 reach closure. Experience showed, however, that just after sunset 

 was the best time, for if the stomata closed at all they usually closed 

 at this time. 



Several days prior to photographing, the strips were transferred 

 to vials containing a saturated solution of Congo Red in absolute 

 alcohol. This stains the cell-walls chiefly, making them stand out 

 very clearly. A number of other stains were tried, but none proved 

 as satisfactory as Congo Red. When ready for photographing, the 

 strip was trimmed and placed upon a special slide with two spring 

 clips which held the cover-glass in place, and then mounted in absolute 

 alcohol. This type of slide was not absolutely necessary, but it was 

 very convenient, because it prevented the strip from floating and the 

 consequent loss of a clear, sharp image. Because of the alcohol 

 mount, an upright camera was used. This consisted of a stand for the 

 microscope, a hood which was tied around the top of the microscope, 

 a camera-box taking a 5 by 7 plate-holder, and a frame which sup- 

 ported all of these. A Spencer microscope was used with a 4 mm. 

 objective, a Zeiss projection ocular No. 2 being used to project the 

 micrograph upon the photographic plate. The same microscope and 

 camera were used for all microphotographs made. The magni- 

 fication (345 diameters) was the largest that could be employed and 

 still have the entire field upon a 5 by 7 plate. 



The photographs of a series were mounted for ready comparison 

 on charts 54 inches square, in the form of a 24-hour clock. Those 

 reproduced are reduced charts made by cutting out an average stoma 

 or group of stomata from each photograph and mounting them on a 

 chart 8 inches in diameter. The light, temperature, and relative 

 humidity curves are given in a circular graph inside the circle of 

 microphotographs. Whenever this circle is a double one, the outer 

 circle shows the upper epiderm and the inner circle the lower epiderm 

 of the leaves of the plant under consideration. In the greater number 

 of series the strips were not photographed, but about 20 stomata of 

 each were measured and averaged to get the material for stomatal 

 graphs. All the charts are not reproduced here, since that would 

 involve needless duplication and bring in species that can not be 

 discussed at this time. 



