MacDOUGAL— HYDRATION AND GROWTH. 361 



ing an incomplete type of respiration which leaves large acid resi- 

 dues. 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 

 situation may also show a marked variation, but within much nar- 

 rower 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 seems to be lacking. It was therefore planned to ar- 

 range a final series of experiments in which the enlargement of 

 fruits with increasing dry weight and others with low relative 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 endo- 

 carp which finally becomes hard and bony with the deposition of 

 anhydrous wall material. The enclosed 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 pulp, 

 which becomes more highly watery as progress is made toward 

 maturity. 



Nuts of Juglans caUfornica var. quercina Babcock, of various 

 sizes from 3 mm. in diameter to that approaching maturity were on 

 two trees in the garden at Carmel 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. Fifteen nuts were 

 measured for periods of two or three days or for as long as two 

 months in the case of No. 10. 



Coincidentally with the measurements an eff'ort was made to de- 

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

 the nuts were borne. A well defined " negative " pressure was de- 

 tected in the basal branches of Juglans major which was growing 

 near the experimental tree. A basal branch 1.2 meters from the 

 trunk gave a dry looking surface when it was cut off. 



