21 



commence to drop leaves before the last week of April, and did not 

 loose 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 vigour- 

 ously growing trees, and A did not seem to be much handicapped 

 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 transpiration, and by 

 means of this and an early leaf-fall it could survive the vicissitudes 

 of the drought. 



I will also briefly relate one of my laboratory experiments, 

 which has a bearing on this matter. Two Castilla seedlings were 

 grown in pots, and when they were four inches high one was placed 

 under a double glass bell, the outer room of this filled with an 

 orange-coloured liquid to give the desired light, and the inner bell 

 constantly filled with well saturated air. The other seedling was 

 placed in a bottomless glass cylinder, and by means of a fan, kept 

 going by a clock movement, a constant exchange of air was secured 

 in the cylinder. This was further placed so that it was exposed to 

 the sun all day long. The roots received all thd water they could 

 absorb, and thus the transpiration was kept at a maximum. First 

 the latter plant was very weak, but gradually recovered strength. 

 After three weeks both plants were examined, both micro- and 

 macroscopically as to latex. The plant in the moist air had well 

 developed latex vessels, but the liquid in these was thin, and with- 

 out any formation of globules. The plant which had been exposed 

 to excessive transpiration had the ordinary latex of young seedlings, 

 but rather concentrated. To make sure that this result was not 

 merely caused by an individual or inherent character of the seedlings 

 employed, I renewed the experiment, taking care to select seedlings 

 which did not appreciably differ in any respect. The result was 

 again the same. 



I consider that this shows that when Castilla is grown under 

 certain conditions the quantity of latex produced in the tree is 

 reduced to a minimum, while under conditions favourable to or 

 assisting excessive transpiration Castilla will produce latex as a 

 means of protection. 



