364 MacDOUGAL— HYDRATION AND GROWTH. 



nights. Finally an abrupt rapid and continuous shrinkage resulted 

 in the separation of the stalk. 



The general features of growth of these nuts may be illustrated 

 by a resume of history of No. lO, which was under continuous ob- 

 servation from July 15 to September 9, 19 18, during which period 

 of 56 days its diameter increased from 16 mm. to 26.5 mm. Of 

 this 2.25 mm. was gained in the first five days of cool foggy weather. 

 This effect was confirmed by the fact that a cessation or retarda- 

 tion occurred at midday and was most pronounced on hot sunny 

 days, suggesting a direct water-loss. In the week ending July 29, 

 the total growth was an increase of 1.7 mm. This period was char- 

 acterized by heavy fogs and mists in the forenoon, both the amount 

 of shrinkage and rate of increase being lessened — an equalization to 

 be ascribed in part to approaching maturity. The temperature taken 

 from a thermometer thrust in a young branch of the thickness of 

 the nut ranged from 13 to 22° C. The completion of the record of 

 No. 10 was followed by cutting of the branch bearing it at a dis- 

 tance of 30 cm. placing excised end in water and arranging the entire 

 preparation in the dark room at 17° C. with the nut under the bear- 

 ing lever of the auxograph. Swelling continued for about 20 hours 

 after which shrinkage began which rapidly accelerated. 



The general features of growth were also well illustrated by the 

 following notes on No. 15, which was brought under observation 

 when it was about 15 mm. in diameter and put under an auxograph 

 amplifying 45 on August 3. Great daily variations in size with a 

 net total increase were displayed every day. Actual enlargement 

 could be detected between noon and 2 o'clock which continued until 

 8 or 10 the following morning, depending upon the sunshine. If 

 the sun rose clear, shrinkage began immediately. If the morning 

 was foggy, it would be delayed, but the increase in thickness was 

 rapid, being mostly accomplished in 2 hours. jNIinor variations in 

 this general procedure might be brought about from the shade of 

 clouds, especially noticeable at noonday August 6 and to be seen at 

 other times (see Fig. i). 



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 



