I06 THE PLANT WORLD 



plants of the same species in adjoining regions fruit at the 

 same or at different periods; and if at different periods, 

 whether the time of fruiting can be corelated with any con- 

 ditions of the environment. We should determine to what 

 extent periodicity is shown by other species of this genus and 

 by some genera of the Dictyotaceee, with the nature of this 

 periodicity, if it exists. It is greatly to be desired that some- 

 one should study, from this point of view, the species of 

 Dictyota occurring on the Pacific coast. All such data will 

 help to answer the important question, whether this phe- 

 nomenon is a very exact reaction to periodic factors in the 

 environment, or whether it is an expression of an inherent 

 tendency of the plant, more or less independent of external 

 conditions. 



It is hoped that this account will indicate the interest- 

 ing nature of the problems involved in this line of investiga- 

 tion, and the great need for more data, and will induce other 

 botanists who are favorably situated to begin a study of this 

 alga. It seems that only by careful observation of the 

 fruiting and by comparison of the conditions at a number of 

 places for a considerable time can we hope to understand the 

 striking phenomenon described. The author will be glad to 

 correspond with anyone who is interested in this problem. 



Johns Hopkins University, 

 Baltimore, Maryland. 



EVAPORATION AND CENTERS OF PLANT 



DISTRIBUTION. 



By Burton Edward Livingston. 



In two previous papers^ attention has been called to the 



effect produced by the evaporating power of the air upon the 



growth of certain plants rooted in a constantly moist soil, 



and to the marked influence which evaporation appears to 



1 Ijivingston, B. E., Evaporation and plant development. Plant W^orld. 

 December, 1907. 



Evaporation and plant habitats. Plant World. Jan., 1908. 



