LIMITING FACTORS TO GROWTH MEASUREMENTS. 365 



The measurements were taken about 8 a.m. and 5 p.m. 

 Thus the day's growth was wholly in the light while the night 

 growth included about 3 hours of light as well as 12 of darkness. 

 The case is clearly one in which water supply is the limiting 

 factor. The days were on the whole bright and sunny 

 and transpiration was energetic. The very much greater 

 growth at night is no doubt due to the fact that with trans- 

 piration almost in abeyance the fruit had a good supply of 

 water. On some days there is actually a contraction in size 

 while the nights show always a considerable increase. 



The case is in fact very like that of Cucurbita measured by 

 F. Darwin (5) and no doubt if sufficiently refined methods of 

 measurement had been employed the smaller fluctuations 

 with changes of humidity would have been marked. 



Whenever there is a period of good water supply the fruit 

 increases rapidly in size and does not show any signs of a check 

 to growth due to insufficient food supply. 



Contrasting with this a series of measurements was taken 

 of several fruits of Artocarpus incisa, the breadfruit. These 

 are borne on young shoots at the ends of the branches. Al- 

 though they may ultimately reach a size of about ^ to i that of 

 a typical fruit of A. integrifolia they do not approach at any 

 time to the rate of growth during the night recorded for the 

 latter species. The fastest rate observed on any night was 

 •48 cms. per 12 hours, and the average was very much less than 

 this being about '2 cms. per 12 hours. So small was the 

 increase in size that errors of measurement became very large 

 and no very great reliance can be placed on the results in 

 consequence. They did show however that though as a rule 

 growth was slightly greater by night, it was very irregular, and 

 on some quite favourable nights the growth was very small or 

 ceased altogether. This may be due to difficulties of trans- 

 location or supply of food material since in other respects the 

 conditions were highly favourable to growth on the nights in 

 question and the fruits of A. integrifolia were as a matter of 

 fact making rapid growth. 



