INTERNAL TEMPERATURE OF LEAVES. 285 



as it is by the numerous examples of deciduous trees mentioned 

 by Wright, is sufficient to justify a search for the cause of the 

 evident connection between dry periods and the production 

 of new growth. 



Of course, such rapid growth as occurs makes much greater 

 calls upon material than can be supplied by the assimilation 

 carried on by the mature leaves during the actual period of 

 growth. Anatomical investigations showed that in every case, 

 just before the new growth appeared, and, indeed, at any time 

 when the tree had had considerable rest after a growth period, 

 the branches and twigs were crowded with starch in the pith, 

 cortex, and parenchyma generally. In the period immediately 

 after grow^th, the older portions of the twigs, from which the 

 new growth had come out, were quite devoid of starch. Thus 

 it was easily shown that this new growth was, as far as starch 

 is concerned, growth from reserve. It may give some idea 

 of the demands made upon this reserve if the rate of growth 

 in length observed in two instances is recorded: 



A young shoot of Brownea ariza gave the following measure- 

 ments : — 



December 17, 10.45 a.m., 20-5 cms. inlengtli; 



18, 2.30 P.M., 25-2 cms. in length; 

 ,. 19, 10.50 A.M., 25 -G cms. in length; 



,. 21, 12 noon, 25 '9 cms. in length; 



22, 3 P.M., 25-7 cms. in length; 



and this length was never afterwards exceeded, though 

 measurements were taken up to January 31. This shoot has 

 evidently been measured just towards the end of its short 

 growth period, but the increase of about 5 cms. during the 

 first day shows the rapidity with which this new growth occurs 

 when at its height. It is interesting too to note that, as far as 

 length growth is concerned, the growth period is of compara- 

 tively short duration , and a length is soon reached which does 

 not increase at all during the long period of rest which follows. 

 The following are the lengths of certain new shoots of 

 Theobroma Cacao measured on three different dates : — 



January 31. February 7, February 15, 



6.5 p.m. 12 noon. 5.50 p.m. 



Cms. Cms. Cms. 



1 15-6 26-0 30-5 



2 .. 8-8 .. 21-2 .. 330 



3 .. 13-5 . 22-6 .. 32-7 



