macdougal: mechanism and conditions of growth 17 



which conformed in its general aspects to the behavior of the 

 previous period. 



The daily increase in length amounted to .6 mm. as a maximum 

 and, as the longitudinal dimension of the joint free of the support 

 was 15 cm., the coefficient of expansion was i in 250 or .4 per cent. 

 On Wednesday, March 17, this increase began at 10 A.M. at 

 63° F. and the expansion followed while the temperature rose to 

 'J2° F. during the next three hours. Some expansion continued 

 with a fall of 2° F. during the next 4 hours. It is evident, how- 

 ever, that the decreasing expansion is not to be attributed chiefly 

 or solely to the temperature relation. This is also supported by 

 the fact that on the following day the increase of a total amplitude 

 of about .4 mm. began at 10 A.M. at 60° F. and went forward 

 rapidly until 3 P.M., the sky having become overclouded at 

 noon, and continued to increase until midnight under the equalized 

 conditions. The temperature remained between 69° and 70° from 

 noon until 6 P.M. and had fallen to 62° F. by midnight. 



That the enlargement in question was not entirely growth, was 

 evidenced by the fact that before the close of the observations on 

 June I a large part of the total increase noted above (2 mm.) 

 had been lost by shrinkage, and the inevitable loss of water during 

 the remainder of the season would probably result in changes 

 similar to those shown by Nos. 2 and 3. (Tucson, 1913-1914.) 



It would appear that the alterations noted above are reversible 

 in greater part and must therefore be attributable to osmotic 

 action and hydratation. 



Not the least remarkable aspect of the matter, however, is the 

 fact that the growth enlargement of joints follows a course fairly 

 parallel to that described. 



The bud of No. 5, for example, began to accelerate at 9 A.M., 

 April 3, temperature 65° F., and followed the rise until 3 P.M. 

 and then slackened (temperature 75° F.), although the temperature 

 continued at this intensity for at least an hour longer. From 

 6 P.M. until 8 A.M. the rate was a straight line and parallel to 

 the temperature record. Acceleration from here lagged, repeating 

 the events of the previous day. (fig. 3.) 



The record of April 6 illustrates another phase. The old joint 

 was undergoing continuous shortening at a fairly uniform rate. 

 Temperature rose from 60° at 6 A.M. to 66° at 11 A.M., varying 

 3 



