138 PLANT WORLD. 



the view that stomata are regulators of transpiration, in the 

 the plants studied. These are not markedly desert types as 

 far as the stomata are concerned, and the amount of water 

 v'apor which may escape through one type of stoma per 

 unit of time may be greater or less than that which may 

 escape through another type. The structure of the stoma, 

 as that of other organs, may indeed explain why some plants 

 are able to get along in the desert, and others not. Stomata 

 of a given form may act as a dampener on transpiration, 

 just as, using an analogy, the mute in a cornet reduces the 

 amount of sound which emerges from the instrument. But 

 the mute does not regulate the sound, causing now more 

 and now less in successive intervals of time. In this sense, 

 also, stomata can not be said to regulate the flow of water- 

 vapor from the leaf. Nor do they "anticipate" wilting, the 

 closure of stomata during this process being as much a result 

 of the wilting as the flaccidity of the other cells of the leaf. 

 We must therefore give up for the present the long cherished 

 notion that stomata are delicate valves opening and closing 

 rapidly to modify the rate of transpiration as the needs of 

 the plant indicate. 



Mazapil, Zac, Mexico. 



EXTRA -FLORAL NECTARIES IN THE CACTI. 



By Francis E. Lloyd. 



The cacti are to be numbered among the plants which 

 possess nectaries other than those which are found in the 

 flower, and it appears that many more cacti than would be 

 expected are characterized by their presence. I have often 

 been surprised by observing very considerable numbers of 

 ants crowding the younger branches of certain of the 

 Cylindropuntiae, even when the plants were not in flower, 

 and this, I believe, is to be explained by the secretion of 

 nectar which is always sought for by ants, and some other 

 insects, when extra-floral nectaries occur. 



