PART II. 



PHYSIOLOGY OF THE STOMATA, WITH SPECIAL REFERENCE TO 

 THE METABOLISM OF THE GUARD-CELLS.* 



NORMAL DIURNAL CHANGES IN THE CONTENTS OF THE GUARD-CELLS. 



(Plate 6.) 



Repeated examination at short intervals, during a period of several days, 

 of the stomata of Verbena ciliata revealed the fact that the amount of starch 

 in the guard-cells was not constant, and further sustained observation per- 

 suaded me that these changes were regular and of such extent that it was 

 possible for one to distinguish with reasonable ease between the stomata 

 taken at one time of the day and another. This result, though borne in upon 

 me only after a prolonged study of the structures in question, was so sur- 

 prising and so at variance with the published results of former observers, so 

 far as I was then acquainted with them, that it was only after about three 

 weeks of further systematic observation that I was finally persuaded of the 

 correctness of my earlier examination. It should be said that at first, at any 

 rate, it is quite difficult to arrive at this result, in part on account of the 

 inability to get a standard of comparison for such small objects as the plastids 

 and their amyloid inclosures, and in part on account of one 's natural skepti- 

 cism when such slight changes are observed. I have, however, taken occasion 

 to show preparations to my colleagues, with the result that the differences 

 were readily seen by them. These differences are, however, great enough 

 to be demonstrable by means of photography, so that the reader has at least 

 representative optical evidence before him. Similar observations have been 

 made, also, upon the ocotillo, but the phenomena in this species are still more 

 difficult of observation. 



VERBENA CILIATA. 



Beginning at sunrise, in the summer time, we find that the amount of 

 starch in the guard-cell is at its maximum. The whole of each plastid, when 

 iodine is applied, colors deeply blue-black. Each plastid contains several, 

 usually from 5 to 7, starch grains, which lie in close contact, the apposed 

 faces of adjacent grains being flattened. The whole group of granules may 



*Presented in brief form before the Botanical Society of America, December, 1905. 



93 



