1899 | VEGETATION OF TROPICAL AMERICA 15 
sandy fields, in the downs, upon the heaths, and in similar locali- 
ties, which at periods are hot and dried up. 
Also in the forests of the tropics one finds these grayish 
hairy leaves especially on lianas, I believe. Among these 
plants a xerophilous construction is not uncommon, and why 
this is the case is easy to understand; for their stems are often 
many meters in length, with a diameter of a few centimeters ; 
they ascend to the tops of the highest trees, clambering from one 
to another, and one may see them hanging like long festoons 
between the trees. Through their slender stems the water is 
to be lifted from one single root up to the leaves ; it has, there- 
fore, an exceptionally long way to travel, and though nature has 
tried to provide for this by making the vessels of the stems, that 
is the water-conduit pipes, wider than in any other plants, it is 
easy to understand that it is, nevertheless, not without benefit to 
the plant to be able to moderate the transpiration. 
In many lianas, as well as in other plants, both in the forest 
and in the scrub, one finds another peculiarity also that is not 
unknown in our northern vegetation, but is much more frequent 
in the tropics, that is, the latex. When cutting through a trop- 
ical scrub every moment one will have an opportunity of seeing 
the latex dripping in large white drops from the wounded stems. 
We do not yet understand the importance of latex in the life of 
plants; different hypotheses have been presented, but none gen- 
erally accepted. Most likely the latex serves several purposes, 
and one of them, I suppose, is to supply water to the leaves in 
times of need, when the transpiration becomes too profuse. If 
the latex tubes really have this task, looking upon them from 
an anatomical standpoint, we must admit that their structure is 
exceedingly suitable to the purpose. 
The scrub also shows other remarkable examples of defense 
against too intense light and profuse transpiration. However, I 
shall mention only one. While wandering in the scrub my atten- 
tion was attracted by the difference between the numerous thorny 
acacia bushes and the other plants. The acacias did not have 
the leathery, dark green, glossy leaves peculiar to so many forest 
