INTRODUCTION. 7 
begins. Chlorophyll is abundant in all parts of the bark, except at the 
short base of the main trunk, so that the death of any part of the tree is 
easily detected by a change in color of the bark from bright green to brown. 
Certain dead twigs were marked, and in the following year the dead region 
was found to have extended farther down the stem, but no case was observed 
where dying had begun below the tip. After a limb is dead it is of course 
impossible to tell the stages by which it died, but the number of dead twigs 
and short dead branches existing on live branches makes it seem probable 
that death begins at the tips and progresses down the stem gradually. The 
death of an entire limb seems in no way to affect the health of the plant as 
a whole. 
As is the case with most of the Leguminose, the plant possesses leaf-' 
movements. During darkness the leaflets are ‘“‘ closed’’— that is, they stand 
with their dorsal surfaces in parallel planes about 0.1 cm. apart—and with 
the coming of daylight the leaflets separate, making various angles with the 
rachis, the “wide-open” position being when the leaflets lie in the same 
plane on opposite sides of the rachis. During cool or moist seasons the 
leaflets remain “open” or partly open during the day, but during the dry 
seasons of spring and fall they close within half an hour after sunrise and 
remain in this position all day, sometimes opening for about half an hour 
near sunset. Leaflets from potted plants that have been well watered open 
wider as a rule in the morning than do those from adult trees and are slower 
in closing. If, however, the potted plants are not given water for several 
days the movements are more like those of the leaflets of adult trees. 
The size of leaflets varies, both in area and thickness, with the age of the 
plant and with the soil and atmospheric conditions existing during the period 
of their growth. On seedlings from one to eight years old the area of one 
side of a leaflet averages 0.04 sq. cm.; on an adult tree the average is 0.02 
sq. cm.; and on hot-house-grown seedlings a year old itis 0.06sq.cm. The 
leaflets which come from very small branches emanating from the main 
trunk near the base are frequently about the same size as those on young 
plants. The diameters are approximately in inverse ratio to the area. 
Figure 1 shows the diameters and arrangement of tissue in leaves of dif- 
ferent types. The different drawings are on the same scale and were made 
with a camera lucida. 
The following differences of structure may be concerned with the trans- 
piration studies which follow. The section of the leaflet from an adult tree 
(A, fig. 1) shows large epidermal cells with heavily thickened walls, stomata 
about midway down the first row of cells, very few intercellular spaces, palisade 
cells and stomata on both sides of the leaf. The section from a plant grown 
all its life in the green-house (C, fig. 1) shows no thickening of the epidermal 
cells, many large intercellular spaces, palisade cells on the dorsal side only, and 
stomataonbothsides. Thesectionfromtheleaf grownin the green-housefor 
a yearand then placed out of doors for six weeks (B, fig. 1) showsastructurein 
several ways intermediate between the other two. The epidermal cells are 
thickened nearly as much as in the section from the adult tree; palisade cells 
