THE PHYSIOLOGY OF STOMATA. 



INTRODUCTION. 



THE POINT OF VIEW. 



The critical study of stomata began with von Mohl. Since his time there 

 have been two trends of study, not always separated, to be sure, but in the 

 main distinct enough so that their recognition serves for the moment a useful 

 purpose in enabling us to define the point of view of the present paper. These 

 are the physical trend of thought, the followers of which have sought to 

 elucidate the mechanical aspects of stomata. Although Schwendener did not 

 ignore the physiological problem, his work was chiefly concerned with the 

 mechanism of the stoma, and we may speak, without injustice to him, of a 

 Schwendener school. 



There are, on the other hand, those who have sought chiefly to determine 

 the causes which underlie the grosser physical manifestations of stomatal 

 activity. Of this physiological school von Mohl himself was the founder. 

 Of late years the chief contributors to the solution of physiological problems 

 pertaining to the stoma are Kohl and Francis Darwin. The latter, especially 

 in his work "Observations on Stomata" (1898), has most trenchantly criti- 

 cized our present knowledge. This paper is brief in its discussions, but 

 masterly and pertinent, and we are indebted to Francis Darwin for showing, 

 at a time when the text-books in general voiced an intellectual complacence 

 on the subject, that, beyond the generally accepted view relative to the role 

 of photosynthesis in stomatal activity dating from von Mohl, practically 

 nothing is understood, and that this view is inadequate to explain certain 

 known facts in regard to stomata. One of these, the opening of stomata in 

 the absence of C0 2 , established by Leitgeb and verified by Darwin, may be 

 cited as an example. To be sure, the attempt has been made to explain such 

 activity by referring the stoma to the class of irritable mechanisms, but unfor- 

 tunately such treatment is not investigation, and does not give us real light. 

 The common point of view upon which the followers of both the physical 

 and physiological students of the stoma have chiefly and naturally stood is 

 that of biological, or teleological, interpretation. Such obvious and striking 

 structures, common to the epidermis of so great a multitude of vegetable 

 organisms, and having throughout a very uniform construction, have rightly 



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