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 thh 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 ou>ter 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 seedfmg was 
placed in a bottomless glass cylinder, apd 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 Jong. The roots received all the 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 inheren* 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. 
