360 smith: application of the theoi;> cm 



the growth was greater in the day than in the night and Sachs 

 oh iii.it this is no doubt due to temperature. Later. 



at the time of greatest growth, the night growth is occasion- 

 ally greater than the day. This is presumably due to lack 

 of sufficient water supply during the day. It will be seen 

 that it is just when the shoot is growing the fastest that the 

 necessary water for so quick a rate of growth would be lacking. 

 and therefore the water supply would be the limiting factor 

 at any rate during the day. During the earlier stages of 

 -lower growth the point when water is lacking is presumably 

 not reached, and it is likely that the temperature is limiting 

 throughout, as in all my observations. 



Sachs (15) also quotes the measurements made by A. Weiss 

 on Agave Jacquiniana Schult (A. lurida Jacq.) at Lemberg. 

 Weiss says that the growth rises and falls with temperature 

 which would bring his results into line with mine, but Sachs 

 states that the figures given do not support this general result, 

 and that the results are really very similar to those of de Vries 

 discussed above. 



Sachs (15) gives as a typical example of his own results the 

 ease of Dahlia variabilis. In this case the stem showed a 

 maximum growth in the morning usually between 7 a.m. and 

 8 a.m.. and a minimum in the afternoon between .'* and 5 p.m. 



The temperature curve which varies from 15° to 21*2° C. 

 i- usually in an opposite direction to the growth curve and thus 

 temperature is not the effective factor in controlling the 

 growth. Sachs himself attributes the afternoon minimum 

 part ly at any rate to \ he Continued and stored up effect of the 



rong lijiht and t he morning maximum to fche absence of lijiht 

 daring the previous night. 



It is however by uo means clearly shown that the humidity 



"t the atmosphere is not the emit rolling factor, for the growth 



in the hotter parts of the day is always slower, while there 



i- an hx through the night when the humidity may be 



opposed bo be increasing. No figures of the humidity arc 



• n f.,i the oighl periods hut it is to be noticed that of those 



