110 



THE AMERICAN BOTANIST 



changes are clue to acids acting on the colors in the plant or 

 whether the changes occur as the result of oxidation pro- 

 cesses seems not to be known for certain. That the latter are 

 likely to be concerned in the matter may be assumed from the 

 fact that the changes occur at the time the plants cease photo- 

 synthesis for the day and therefore cease giving off oxygen, 

 and occur again when the process is resumed. It is probable 

 that when light returns and the plant resumes the exhalation of 

 oxygen, this gas oxidizes some of the cell sap and the pink 

 color returns. The subject is one that ought to prove of inter- 

 est to the organic chemist. 



Influence of Trees on Rainfall. — There are two 

 ways in which forests may affect the rainfall. It is conceded 

 by everybody that wooded areas lessen the danger from floods 

 by holding back the fallen water and obliging it to flow away 

 gradually, thus keeping the springs full and the streams flow- 

 ing, even in dry weather, but whether the forests can induce 

 a heavier rainfall in their vicinity has been a point upon which 

 there has been much argument in recent years. Our meteoro- 

 logical experts practically agiee that forests have no effect on 

 the amount of the rainfall, but now comes Raphael Zon of 

 the United States Forest Service with the statement that 

 forests not only do affect the rainfall, but that they supply 

 most of the moisture that falls on a large part of the United 

 States, all of which he backs up by rather convincing evidence. 

 His contention, in brief, is that since the rainfall ultimately 

 runs back to the ocean, the ocean must be the original source 

 of supply but that the moisture-laden winds from the ocean 

 cannot carry this moisture to the interior of the continent. 

 Most of the moisture that falls in the Mississippi Valley comes 

 from the Gulf of Mexico or the Atlantic ocean but the winds 

 blowing inland drop this moisture as rain before they have 

 gone far. The rain that falls farther inland is the moisture 

 evaporated from vegetation nearer the coast and this moisture 



