macDougai^hydration and growth. 



369 



The actual volume of this fruit at the close of the experiment 

 was approximately 2,200 cu. mm. and its growth had been followed 

 for a period of 40 days. It is notable that in the earlier stage in the 

 advance of the fruit from 20 to 26 mm. in diameter that while the 

 increase of the diameter seems constant yet the actual accession of 

 material is very much greater. Then in further development the 

 average increment to the diameter was smaller, yet the actual ac- 

 cession of material was greater. Following this the rate falling 

 from 0.8 to 0.3 mm. daily the accession decreases less than half. 



The record of growth of No. 3 shows beyond question the effect 

 of transpiration and water loss on growth. As the daily tempera- 

 tures of the fruits rose fromi 12° C. and 14° C. to 26° C. and 28° 

 C, acceleration ensued up to a point where the rise caused a water 

 loss overbalancing the gain by hydration. Higher temperatures 

 therefore did not facilitate or accelerate growth unless accompanied 

 by high relative humidity. Thus the highest are those of midday 

 and afternoon, with fog or showers. This is especially marked on 



Nn \fi Hn WIV Nn U\ Hn H\ Mn Mt 



Fig. 2. Auxograph tracing of variations in volume of fruit of hybrid 

 solatium. Downward course of line denotes enlargement amplified 45 times. 

 The scale is numbered in millimeters. Midday temperatures are given. 



the record of September 10, ii, 12 and 13, in which a 50-hour rainy 

 period was anticipated and followed by high humidity. It was not 

 possible to increase the water supply by watering the soil around 

 the roots in such manner as to cancel the midday shrinkage or slack- 

 ening in growth. One especially striking effect is that in which the 

 rise in temperature consequent upon the cessation of the rain from 



PROC. AMER. PHIL. SOC VOL. LVIII. X, NOV. 28, I919. 



