STEPHEN HALES 127 



very much smaller than, Sachs' result with the 

 sunflower, viz. 63 cm. per hour. 



The data are however hardly worth treating in 

 this manner. But it is of historic interest to note 

 that when Sachs was at work on his Pflamen- 

 physiologie, published in 1865, he was compelled 

 to go back nearly 140 years to find any results with 

 which he could compare his own. 



We need not follow Hales into his comparison 

 between the "perspiration" of the sunflower and 

 that of a man, nor into his other transpiration 

 experiments on the cabbage, vine, apple, etc. But 

 one or two points must be noted. He found^ the 

 "middle rate of perspiration" of a sunflower in 

 12 hours of daylight to be 20 ounces, and that 

 of a "dry warm night" about 3 ounces ; thus the 

 day transpiration was roughly seven times the 

 nocturnal rate. This difference may be accounted 

 for by the closure of the stomata at night, a 

 phenomenon unknown to Hales. 



Hales* notes another point which a knowledge 

 of stomatal behaviour might have explained, viz., 

 that with "scanty watering the perspiration much 

 abated " ; he does not attempt an explanation, but 

 merely refers to it as a "healthy latitude of perspira- 

 tion in this sunflower." 



In the course of his work on sunflowers he 

 notices that the flower follows the sun. He says, 

 however that it is "not by turning round with the 

 sun," i.e. that it is not a twisting of the stalk, and 



* Vegetable StaUcks, p. 5. 

 ' Ibid., p. 14. 



