NORMAL STOMATAL MOVEMENT. 1 03 



stomata were observed which could be said to belong to i or 2. These gen- 

 eral differences can be told at a glance, when the mind is not prejudiced, 

 for the preparations were examined by an observer who did not know what 

 the objects were, and he recognized the differences at a glance. 



Just as it is difficult to distinguish between two adjacent grades of starch 

 dissolution in neighboring stomata, so also is it difficult to recognize any 

 difference in stomata taken at short intervals apart. The difference between 

 stomata taken at 3 a. m. and 8 or 9 a. m. is marked enough, but between 

 3 and 5 a. m. the difference is more difficult of recognition. There is a differ- 

 ence, however, recognizable under the lower power of magnification, as a 

 difference in depth of staining, and in part to the smaller size of the starch 

 granules, which therefore do not crowd upon each other as densely (approxi- 

 mately as seen in plate 8, fig. 3), thus allowing more light to fall between 

 the plastids, and also between the granules within the plastids. 



That these differences are real and of significance is indicated by the fol- 

 lowing observations made October 18, 1906, at 9 h 3o m a. m., on the stomata 

 of a potted plant of ocotillo, on leaves a few days old but still tender. The 

 stomata were all in the young condition, showing little secondary develop- 

 ment, and were open from 3 to 6 micra. I plotted a group of 8 or 10 stomata, 

 two of which in the center were 6 micra open, while those surrounding were 

 3 micra open. Upon irrigating with water they all closed, and upon adding 

 iodine, all under continual observation, the reactions in the two 6-micra sto- 

 mata were sensibly less marked than in the surrounding ones. 



Wortmann regards corrosion of the starch grains as necessary evidence 

 to the conclusion that starch is being digested. I was, however, not able 

 to observe any pittings such as are usually observable in large starch grains 

 (e. g., potato) on digestion by diastase. It is possible that the starch grains 

 of the guard-cells are not corroded irregularly, as is often the case, but are 

 gradually dissolved from without with the same rapidity at all points. This 

 is what appears actually to occur in the guard-cells. In dead guard-cells, 

 for instance, the starch granules are frequently perfectly spherical in form, 

 while their appearance otherwise indicated clearly that they are in an arrested 

 state of partial dissolution, and I have noted similar appearances in the nor- 

 mal guard-cells at about 9 a. m. The individual granules of a plastid are 

 separated from each other by double-concave masses of the plastid matrix, 

 as if the starch disappeared before the plastid became reduced in size ; while, 

 when the starch granules are growing, these are separated by plane masses 

 of the plastid matrix, suggesting that the centers of starch accumulation were 

 close together at first, thus bringing the starch granules into close juxtapo- 

 sition. The very small size of the starch granules, however, makes their 

 observation in this regard very difficult, and these statements must therefore 

 be regarded as tentative. 



