6 THE PHYSIOLOGY OF STOMATA. 



been looked upon as important in placing the protoplasts within the leaf or 

 plant in contact with the above-ground environment. To allow chiefly the 

 entrance of light, the exit and escape of gases, or the escape of water-vapor 

 have been emphasized separately or collectively by almost every observer. 

 With the exception of the first, which may now be disregarded, these are to 

 be admitted as qualitatively true. In view of the suppression of gaseous dif- 

 fusion through the cuticle, the stomata are certainly the sole path by which 

 gases, in wide sense, enter and escape (Blackman, 1895). And that the loss 

 of water by the plant is chiefly through the stomata is also true. The more 

 difficult question of what the exact biological meaning of the stomatal move- 

 ment is, has not been answered quantitatively. Schwendener's contention 

 that, inasmuch as the plant is normally active only when fully supplied with 

 water, and that, therefore, the stoma has to do with the interchange of oxygen 

 and carbon dioxid, appears rather to avoid the issue. On the other hand, 

 those who see in stomata mechanisms intimately connected with the control 

 and regulation of the passage of water-vapor from the plant, have not suc- 

 ceeded in advancing facts in support of their position. Certain phylogenetic 

 considerations* fail to offer more than suggestions, and can not be expected 

 to do more, since at all times photosynthesis in, and the escape of water from, 

 the aerial parts of green plants, whether gametophytic or sporophytic, have 

 gone on hand-in-hand; and, moreover, the plants of the past are now not 

 available. The problem, in its quantitative aspect, must therefore be solved 

 by physiological methods and the answers to specific questions so attached 

 will bear upon physiological problems, purely considered, and upon the 

 biological question above indicated. 



Regarded in this way, the problem of stomatal activity is by no means a 

 slight one. The attempt in the present paper has been made to attack it on 

 two points: (i) Specifically, the supposed relation between stomatal move- 

 ment and the loss of water-vapor by the plant, in order to determine whether 

 this loss is regulated by the stomata; and (2) the determination, so far as 

 possible, of the cause of stomatal movement, or more particularly, the cause 

 which leads to a rise in turgor greater than that in surrounding cells (Kohl, 

 1895), which results in the opening movement. 



The series of studies which are here brought together was begun in the 

 summer of 1904, under the valued patronage of the Botanical Society of 

 America, at the Desert Botanical Laboratory; at the same place, during the 

 following summer, by means of a grant from the Carnegie Institution of 

 Washington; and during the major portion of the present year (1906), while 

 the author was a member of the staff of the Desert Botanical Laboratory. 



*Cj. K. Goebel: The Present-day Problems of Plant Morphology. Transl. by F. E. 

 Lloyd, Science, n. 



