211 



atures, near one of the trees standing about in the middle of the 

 group of trees measured. I intended to return two hours later, 

 when the full heat of the sun had been acting on the trees to re- 

 measure the trunks in order to find out the shrinkage of the trunks 

 at different times of the day. I was delayed, and returned some 

 four hours later instead, at 10. 47 a.m. The first thing I noticed 

 was that one of the trees which in no way differed from its neigh- 

 bours upon my first visit, was now looking very exhausted, with 

 drooping branches and leaves hanging limply downwards. An- 

 other tree standing by looked perfectly fresh, while some of the 

 others showed signs of having been slightly affected by the now 

 scorching rays of the sun. This difference in power of withstand- 

 ing sudden high temperature was so marked that I decided to try 

 the different trees for latex. The result of a small cut in each 

 tree was that A, the tree with drooping leaves, had no latex, 

 while H, the most fresh looking tree of the lot, had plenty. 

 Between these B, C, etc., showed a gradual increase in the amount 

 of latex with the exception of two trees F and G, of which the 

 latter had less latex than the former, but it was much thicker. 

 This year I noticed the same difference at the end of January. 

 Closer observation now revealed the fact that A had much more 

 hairs on the leaves, petioles, and branchlets than H, and thus 

 ought to have been better protected against too rapid transpiration, 

 Counting the stomata on the leaves, I found that the number was 

 smaller in A, — another protective device. The barkpores were 

 almost equal. Five weeks later A commenced to drop its leaves, 

 and was almost bare at the end of March, when H still had 

 all its foliage left. H did not commence to drop leaves before 

 the last week of April, and did not lose many before the rainy 

 season set in, and new leaves were again developed. A recovered 

 rapidly in June, after the rains began, and was soon clothed in 

 full foliage. In January, A had a small amount of latex, and 

 whenever cut during the dry season a few drops appeared in the 

 wound. After a few weeks of rain no latex appeared from an 

 incision, i.e., the tree behaved exactly as it had done in the rainy 

 season of the previous year. H had an abundant supply of latex 

 in the wet season, and in the dry part of the year this latex was 

 still present, but was less watery, or more concentrated. 



How are we to explain this fact that a tree, such as H in the 

 above experiments, with less of ordinary protective devices, but 

 more latex was better able to stand excessive transpiration than A, 

 with rather well-developed protective arrangements, but only 

 little or no latex ? I think the only answer is to be looked for in 

 the presence or absence of latex in respective trees. Both were 

 vigourously growing trees, and A did not seem to be much handi- 

 capped by the absence of latex, except in regard to transpiration. 

 When having the advantage of a humid atmosphere and plenty 

 of water after the beginning of the rains, the tree grew as well, 

 and almost better than the others. It is also worth noticing that 

 in the dry season a small amount of latex appeared. It was all the 

 tree was able to produce for its protection against rapid transpi- 



