THE AMERICAN BOTANIST. 115 



vantage in the evolution of such species is still problematical. 

 The whole willow and poplar alliance have dioecious flowers 

 and might fonn good subjects for experiment along this line. 

 The power to produce the structures lacking in each type of 

 flower is doubtless latent in each plant if one could discover 

 the conditions necessary to bring it out. 



Function of Stomata. — In all the higher plants the 

 leaves are covered with a thin skin or epidennis that is nearly 

 impervious to water and air, but since the vital processes of 

 the leaf cannot go on without access to the surrounding air, 

 the epidermis is provided with millions of small openings 

 called stomata. These consist of two, usually crescent-shaped, 

 cells which are currently supposed to open and close as the 

 needs of the plant require. In dry air they were expected to 

 close and thus retain the moisture of the leaf, but in moist air 

 they were supposed to open and allow transpiration. Every 

 book on botany makes this statement but like so many other 

 things in botany that have been taken for granted, it is now 

 known to be incorrect. Whatever else the stomata do, they do 

 not open and close in response to varying amounts of moisture 

 in the air. 



Seed Dispersal in Polygonum. — It is a common failing 

 with scientists to over look any publication that does not make 

 great pretentions to authority. In consequence many botanical 

 facts that may be well known are again "discovered" by scien- 

 tists who do not take the trouble to look up the literature of 

 the subject. An instance of this came to notice recently in a 

 publication by two botanists with the suggestive names of 

 Reed and Smoot, in which the seed dispersal of the Virginian 

 knot-weed {Polygo)iuiii Virginimium) is discussed. Essent- 

 ially the conclusions they make were published in Kerner & 

 Oliver's "Natural Histoi-y of Plants" many years ago. In 

 substance the principal method of dispersal is this. The fruit 



