102 



THE PHYSIOLOGY OF STOMATA. 



FOUQUIERIA SPLENDENS. 

 VARIATION IN THE STARCH CONTENT OF THE GUARD-CELLS. 



After satisfying myself that the observations on the increase and decrease 

 of starch in the guard-cell of Verbena were, so far as I could judge, correct, 

 I very naturally hoped that I might succeed in finding instances among other 

 plants which would afford evidence of the same kind. With this in mind I 

 examined at various times of the day a number of species (Amaranthus, 

 Jatropha, Nicotiana, Euphorbia, etc.) without finding sufficiently constant 

 differences to afford a basis for comparison with Verbena. Upon confining 

 my attention exclusively to one species, the ocotillo, and comparing series of 

 observations made at considerable intervals of time, the conviction grew 

 upon me that in this plant, too, there is a regular, though less obvious, change 

 in the amount of starch, the maximum being reached in the night (or perhaps 

 the early hours of the morning before sunrise) and the minimum during the 

 latter half of the forenoon. The data in table 50 were gathered by examining 

 pieces of epidermis taken from the same plant at 3 h 2o m a. m., 8 h 3o m a. m., 

 and 6 h 30 m p. m., and grading the stomata with reference to the amount of 

 starch found in them. 



Table 50. — The change in amount of starch in guard-cells of ocotillo, July 27, 1906. 



It was found that the stomata could be grouped in five groups in a series 

 from "starch meager" to "starch very abundant." The maximum amount 

 of starch in the ocotillo stoma is very much greater than in the verbena. The 

 groups were numbered, for convenience, from 1 to 5. The counts were made 

 by chance by moving the slide in one general direction and estimating the 

 condition of all the stomata in the field at one time. The summations of 

 counts only are given. 



The figures in table 50 must be regarded as representing approximation 

 only. It is difficult to distinguish always between the condition of the sto- 

 mata in any two grades, and one must make counts at random, judging as he 

 goes. But it is not difficult to distinguish between grades 1 or 2 and 4 or 5. 

 The accompanying figures (plate 8) show the extreme observed contrast 

 between 3 h 2o m a. m. and 8 h 30 m a. m. The table shows that in the 3 h 2o m 

 a. m. piece there were no stomata approaching the 8 h 30 m a. m. condition; 

 while in the 8 h 30 m a. m. piece there was a small majority approaching or 

 equaling the condition of the 3*20™ a. m. stomata. In the 6 h 30 m p. m. 

 piece a general change towards the 3 h 2o m a. m. condition is evident, as no 



