9 8 



THE PHYSIOLOGY OF STOMATA. 



the plant Verbena ciliata the oil is present in the stomata in appreciable 

 quantities only for a small portion of the day. At sunrise the amount is very 

 small and optically quite inappreciable, except as minute droplets, which 

 would defy identification by the casual observer except by refined methods. 

 During the period in which the stoma is opening, however, the droplets in- 

 crease greatly in size until usually one, but often two, large drops are found in 

 each guard-cell. Smaller ones, too, may frequently be seen. One large drop 

 near the end of the guard-cell is the characteristic condition (plate 6, fig. 5). 

 Their nature is demonstrated by their behavior in potash, in which they 

 become irregular in shape, and apparently of a soapy texture. They take up 

 alcannin readily ; potassium iodide-iodine renders them very transparent and 

 difficult to see, ultimately becoming shriveled and dissolved, while alcohol 

 renders them opaque, often with a slightly crenate or irregular margin. After 

 treatment with alcohol they may sometimes appear as if cracked on one side, 

 suggesting that a hardening or coagulating effect has been induced. In the 

 afternoon, i. c., during the closure of the stomata, the drops wane, until by 

 jh-^o™ or 2 o'clock they have been reduced to minute droplets of the size seen 

 at daybreak. Nor do they at any time reappear till the following day. The 

 constancy of these changes is so marked under normal conditions that, in 

 view of the similar but reversed changes in the starch content, the suggestion 

 presents itself that there is a direct connection between these two substances. 

 This is, however, entirely unlikely, as will later be shown. It is of very 

 considerable interest in this connection to note that Leitgeb (1888) found 

 that the oil-drops of Galtonia stomata gradually disappear when starved by 

 isolation, and it is probable that further study of this plant would throw light 

 on the difficult problem of the significance of this substance in the stoma. 

 The data in table 48, extracted from notes recorded in July, 1905, serve to 

 indicate the basis for the foregoing description of the changes which occur 

 within the guard-cell, as well as to present the results in summary form. 

 The original wording has been preserved in condensed form. 



Table 48. — Changes in contents of guard-cells and of pore. 



