THE EFFECT OF CLIMATIC CONDITIONS ON THE 
RATE OF GROWTH OF DATE PALMS 
A. E. VINSON 
(WITH ONE FIGURE) 
The observations on which this study of the effect of climate 
‘on the rate of growth of date palms is based were made at the 
Cooperative Date Orchard, Tempe, Arizona, by F. H. Smmmons, 
at the suggestion and under the supervision of Director R. H. 
Forses of the Arizona Agricultural Experiment Station. The 
length of every leaf on four palms—two Deglet Noors and two 
Rhars—was carefully measured weekly during 1906 and 1907- 
By the system adopted the maximum error did not exceed one- 
quarter inch. In addition to the leaf measurements, daily records 
were kept of maximum and minimum atmospheric temperatures, 
and of soil temperatures at one foot, three feet, and five feet below 
the surface. A record of the level of the ground water was also 
kept, but this factor probably had no influence on the rate of 
growth, since the deeper roots were immersed in water at all times 
throughout the two years. 
The data representing the weekly growth of all the separate 
leaves are too voluminous to use in their entirety. In most cases, 
after a new leaf has emerged well from the central bud, it makes 
the greater part of its growth in five or six weeks. After that the 
weekly growth, as shown by elongation, becomes much less, and 
finally appears as a negative quantity. This is due to the base 
of the leaves surrounding the entire stalk, which, as it expands, 
tends to draw the leaf as a whole lower down on the stalk. After 
repeated trials to obtain from this mass of data a series of consistent 
and comparable figures representing weekly growth, it was found 
that the sum of the elongation of the inner five leaves, that were 
unfolded sufficiently to be measured, gave the most satisfactory 
series. These were then calculated for each of the four palms am 
plotted as a curve, the ordinates of which represent the weekly 
growths (fig. 1). The maximum and minimum daily temperature, 
Botanical Gazette, vol. 57] [324 
