STOMATA DURING WILTING. 87 



He states: 



The epidermis which prevents the escape of water- vapor also prevents the absorption of 

 carbon dioxid. This difficulty was surmounted by the formation of stomata. A leaf 

 without stomata, or what is the same thing, with its stomata permanently closed, as with 

 wax, will not lose water, but it will starve for want of carbon dioxid. The stomata are open 

 so long as there is no danger of such a water loss as would result in loss of turgidity, but 

 when the cells show an approach to flaccidity the stomata close [italicizing mine]. 



Originally the loss of water was harmful, but many plants have in a second- 

 ary way made use of the stomata for the purpose of obtaining with the trans- 

 piration stream a supply of materials for use in building up the tissues and 

 for other purposes. To the support of Bessey's view may be brought the 

 lack of regulatory function of water loss by the stomata, at least to the extent 

 that, though they allow the escape of water, they have not become so far 

 adapted secondarily to regulate it. But, after all, the harmfulness of water 

 loss by primitive plants is an assumption, as there may never have been a 

 time in the history of plants when some transpiration was not a useful process, 

 the hindrance of which would have delayed the progress of necessary physio- 

 logical change within the plant. It seems to be simpler and more in accord 

 with the known facts to regard the stomata as a means of communication 

 between the interior of the plant and the gaseous environment, and that their 

 function is to allow the exit and entrance of gases, inclusive of water-vapor. 



