166 



Hydration and Growth. 



day to 0.7 mm. when shaded on August 6, and to a similar amount in 

 a rain on September 11, at which time it was in an advanced state of 

 development (fig. 49). 



It is to be seen from the above that the fruit of the walnut in an 

 environment favorable to its development exhibits daily variations in 

 growth clearly attributable to the balance between transpiration and 

 absorption. The nut in a growing condition has a high water-content 

 and a small unsatisfied capacity, but its supply from the relatively 

 dry stems must come slowly — so slowly that any marked increase in 

 transpiration would overbalance the absorption by the nut and result 

 in cessation of enlargement or even shrinkage. 



lZp.m. 



Fig. 49. — Variations in volume of a growing nut of Juglana 15 mm. in diameter at beginning 

 for a period of 45 days. The marked acceleration under the conditions of high humidity 

 and abundant water-supply are illustrated in the record beginning September 9. Retarding 

 or shrinking effects of noonday temperature and low humidity and masking effects of fog 

 are also illustrated. 



The fruit of the tomato {Ly coper sicon) presents features of water- 

 content unlike any other organ the growth of which had been under 

 observation in present studies. The most striking feature of this 

 phase of the matter is that the proportion of solid material is higher in 

 young fruits than in mature ones. In the determination of the pro- 

 portions, first young fruits less than a week old were taken and 4 

 tomatoes with radial diameters of 14, 16, 17, and 18 mm. were found to 

 weigh 14.650 grams. These were fragmented and placed in a beaker 

 on a water-bath at about 100° C. for 48 hours, at which time the dry 

 material remaining was 1.90 grams. From this it is to be seen that the 

 young fruit contained 87 per cent of water and 13 per cent of dry 

 material. A mature fruit of the same kind as those measured was 

 46 mm. in axial diameter and 58 mm. in radial diameter and weighed 

 93.050 grams. This was dried over water-bath for 2 days, at which time 



