162 Hydration and Growth. 



type of respiration which leaves large acid residues. These, con- 

 stituting the total acidity of the cell-masses, may vary greatly during 

 development and during the course of a day, and the actual acidity or 

 hydrogen-ion concentration of the sap resulting from the buffer situa- 

 tion may also show a marked variation, but within narrower limits. 



Although the development and maturation of fruits such as berries 

 obviously includes a growth in which the total effect is one of practical 

 maintenance or increase in the water-content, studies of their growth 

 seem to be lacking. It was therefore planned to arrange a final series 

 of experiments in which the enlargement of fruits with increasing dry 

 weights and with small and more nearly constant dry weights should 

 be measured. The walnut was taken to represent a structure with 

 accumulating solid matter and the tomato for the other type. 



The walnut consists of a thick, fleshy exocarp and a heavy endocarp 

 which finally becomes hard and bony with the deposition of anhydrous 

 wall material. The inclosed embryo also accumulates a large amount 

 of condensed food-material. The tomato is a large globose berry in 

 which deposition and thickening is confined to the small, hard seeds. 

 The greater part of the fruit is a fleshy, watery pulp, which becomes 

 more highly hydrated as progress is made toward maturity. 



Nuts of Juglans californica var. quercina Babcock, of various sizes 

 from 3 mm. in diameter to that approaching maturity, were borne on two 

 trees in the garden at Carmel, California, in June 1918. Suitable supports 

 being provided, the bearing lever of an auxograph was rested as lightly on 

 the young nuts as was consistent with a clear record, and temperatures 

 were taken by thin thermometers thrust into similar nuts or into young 

 stems near the preparation. 15 nuts were measured for periods of 2 

 or 3 days, or for as long as 2 months in the case of No. 10. 



Coincidently with the measurements, an effort was made to determine 

 the degree of saturation or hydration of the stems on which the nuts 

 were borne. A well-defined "negative" pressure was detected in the 

 basal branches of Juglans major, which was growing near the experi- 

 mental tree. A basal branch 1.2 meters from the trunk gave a dry- 

 looking surface when it was cut off. 



A section of a similar branch about 8 mm. in thickness and 42 cm. 

 long was cut away from another basal branch of the tree, the end of the 

 detached portion quickly sealed with vaseline, and when all was in readi- 

 ness the tip was excised and the cut thrust into water to ascertain the 

 actual deficiency in this portion; 14 hours later a total of 6 c. c. of 

 water had been absorbed and 24 hours later 8.5 c. c., which was a practi- 

 cal saturation, at a temperature of 18 to 20 C. The volume of the 

 branch proved to be 35 c. c., so that the amount of water absorbed was 

 24 per cent of the total. 



Sections of young internodes of Juglans californica quercina which 

 had an average diameter of about 2.5 mm. were swelled in solutions as 



