ST(JM.\T.\. 133 



piece, and certain of his drawings are now to be found In 

 almost every botanical text-book. He shcnvcd especially how 

 the stoma works, as a machine, and laying aside the physio- 

 logical part of his work in this Held, the Impetus which he 

 gave to the study of the stoma is due chiefly to this. In our 

 own country, Copeland studied a considerable number of 

 kinds of stomata, extending our knowledge of their manner 

 of working. 



As to the way in which the stoma serves the plant, 

 every possible view has been held. It was early thought 

 that it was their function to allow the entrance of light into 

 the Interior of the leaf. This indeed they do, but now we 

 know that the cuticle does so, and that, were the stomata 

 all plugged with an opaque substance, there would be but 

 the merest amount of Interference to the passage of light. 

 That these organs allow the escape of water vapor, and 

 the entrance and exit of gases are facts. But whether the 

 primary object Is to allow the escape of water, or to establish 

 a sufficiently Intimate relation between the Interior of the 

 plant and the surrounding atmosphere Is still debated, the 

 weight of opinion appearing to be, at present, on the side 

 of those who contend that the plant is trying to save its 

 water-supply, and at the same time to give out and take In 

 the gases Involved In Its protoplasmic activity. But the 

 view that the stomata are the "regulators of transpiration" 

 is not without Its supporters and the fact that they open and 

 close Is a fact which seems to corroborate this Idea. It has 

 been supposed that this opening and closing Is closely corre- 

 lated W'ith the amount of water vapor which escapes, and 

 that when the amount of vapor escaping Is too great, thus 

 tending toward undue loss and consequent wilting, the 

 stomata close, with the result that the danger Is averted, to 

 an extent sufficient at least to off-set danger which Is not 

 too great. It was the writer's task to begin In 1904 a study 

 of stomata with the view of testing In particular the Idea 

 that transpiration is regulated by the opening and closing of 



