130 REPORTS ON INVESTIGATIONS AND PROJECTS. 



The stomata are most nearly shut early in the morning, before 

 dawn. They are normally only partially closed at night. After sun- 

 rise they slowly open till 8 or 9 a. m., after which they slowly close, 

 but only so much as to contract the opening to perhaps one-third its 

 transverse diameter. 



Contrarj' to the general belief, the plastids of the guard cells are 

 not provided with chlorophyll, and this appears to be true of many 

 other plants. There is conclusive evidence also that the physiology 

 of the guard cell is quite different from that of the chlorenchyma cells 

 of the leaf. In the latter the accumulation of starch occurs during 

 daylight, commencing at sunrise and increasing during the day 

 till nightfall. Conversely, during the night the starch thus accumu- 

 lated slowly disappears, and is absent from the plastids by daybreak. 

 In the guard cells, however, the starch found at nightfall does not 

 disappear from the plastids, so that at daybreak it is abundant. 

 During the hours between daybreak and 9 a. m, , or somewhat earlier, 

 the starch content gradually disappears, until little or none is visible. 

 At the same time an oil, not present (or if so in inappreciable quan- 

 tities) at dawn, accumulates until large drops of it are present, usually 

 one in each cell. They are easily mistaken at first for nuclei, but 

 their resemblance to these bodies is merely superficial. This oil 

 slowly disappears again until, at the close of day, it is absent, or 

 if present is in inappreciable quantities. During this same period, 

 namely, from 9 a. m. till sunset, the starch content is increasing, 

 but experimental inquiry indicates that this accumulation of starch 

 is not dependent, w^holly at least, upon the presence of light, nor 

 directly to the presence of carbon dioxide. These conclusions point 

 very directly to the necessity of turning attention to the internal phys- 

 iology of the guard cells. 



The methods employed were those previously devised during the 

 summer of 1904, and were described before the Botanical Societj' of 

 America at the Philadelphia meeting, 1904-1905. 



Olivet Edgfar W., University of Wisconsin, Madison, Wisconsin. 

 Grant No. 271. Researches on the life histories and cytology oj 

 ccrtaiji lower plants. (For previous reports see Year Book No. 2, 

 p. xxvii, and Year Book No. 3, p. loi.) $i.ooo: 



Abstract of Report. — Two papers, representing the writer's earlier 

 work as an associate of the Carnegie Institution of Washington, have 

 been published during the year — one on the structure of the blue- 

 green algae and one on Monascus. Two other articles are in press — 



