MacDOUGAL— HYDRATION AND GROWTH. 367 



cultural requirements of these plants. The results may be best set 

 forth by the description of the action of the several fruits measured. 



No. I was placed in the greenhouse and a fruit 29 mm. in diam- 

 eter was fixed on a block of hard cork in such position that it gave a 

 radial bearing to the auxograph which was set to amplify changes in 

 volume by 5, on August 9. The record was kept continuously until 

 September 18, at which time the radial diameter of the fruit was 

 51.5 mm. The fruit was turning yellow on September 16 and was 

 showing fluctuations in volume comparable to those in No. 2, with 

 which it was run in close comparison and under almost exactly the 

 same conditions of moisture and temperature as recorded. 



No. 2 was adjusted to the auxograph in the greenhouse on 

 August 9 in such manner as to give modifications of the axial diam- 

 eter, which at this time was about 27 mm. The record was con- 

 tinuous until September 18, at which time the diameter was 50.5 

 mm. This fruit like No. i was beginning to turn yellow on Sep- 

 tember 16. 



No. 3, 10 mm. in diameter, was adjusted to the auxograph to 

 record variations in radial diameter on August 21, and a record was 

 kept continuously with frequent notations of temperature and sun- 

 shine, etc. It is to be noted that i, 2 and 3 were under equable tem- 

 peratures, 19 to 20° C, and high relative humidity during the rain- 

 fall of September 11 and 12. 



The fact that the greatest increase in growth occurs in fruits at 

 diameters between 16 to 25 mm. in diameter, before half the final 

 size is reached is a point to which we shall recur in the discussion 

 of growth in terms of volume. Thus in No. 3 the increases in thick- 

 ness weekly were as follows : 6 mm., 6.3 mm., 2.5 mm., 3.5 mm. 



If this method be followed it would at once be obvious that while 

 the rate of increase in diameter would be a direct measurement yet 

 as the fruit increases as a globe the actual material added could be 

 regarded as a shell on this globe. The rate in terms of volume 

 would therefore be the amount of this shell to be calculated by find- 

 ing the difference between the initial volume, and the volume at the 

 end of each period by the formula Pi r — Pi R in which r^the 

 new radius and R the initial radius. The rate by direct measure- 

 ment of diameter and by volume increases may be compared as 

 below. 



