456 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
pinnae closely appressed, maintaining a growth rate as one indi¬ 
vidual. The form suggests an acutely sharpened stake for which 
the writer proposes the name palus, from the Latin pains, a stake. 
This palus or synchronous group of leaves may be extruded to a 
length of 2 or 3 feet before the new growth from within separates 
them and they assume an individual rate of elongation. 
EXPERIMENTAL DATA 
METHODS OF THE EXPERIMENT 
In order to determine the various questions of growth in relation 
to light and temperature, seven seedling trees at the United States 
Date Garden at Indio, Calif., were selected for observation. 
As the palus of new leaves emerged from the buds of two of these 
selected individual leaves were marked into 1 cm. and 10 cm. divi¬ 
sions, in- order to learn whether any further elongation was made. 
The length of unexpanded pinnae was also recorded to learn whether 
they had attained their full length. In no case was any further 
elongation of light-exposed portions of either rachis or pinnae ob¬ 
served. A varying portion of the leaf was pushed up daily from the 
heart of the bud, the movement of which will be discussed later. 
The depth at which actual elongation of the tissue was taking place 
could only be surmised from external observations. 
Next a discarded male tree about 5 years old was dissected in order 
to trace the elongation to its source. A sector of one-third of the 
circumference was cut out to 10 inches below the top of the bud, 
and two-thirds of the radius toward the center. Without invading 
the very center of the bud, portions of the bases of several of the 
younger leaves were reached where the tissue was ivory white, the 
fibrovascular bundles yet unhardened, and the whole substance easily 
broken with a square brittle fracture. While these dissections were 
being made, the admirable binding quality of the fibrous older sheaths 
was at once apparent. The whole central part of the bud was in a 
state of tension from the turgescence of the growing parts within. 
A distinct popping sound could be heard as the tensely strained layer 
of “leef” or sheath fiber was severed with a quick cut of the knife 
and the pressure within relieved. If the leaves in the bases of which 
lignification had not taken place were not supported at once, they 
were broken by the slightest swaying by the wind or overbalanced 
by their own weight. Ten-centimeter portions were marked in centi¬ 
meters on the succulent exposed portions of five such leaves, and 
these again marked in millimeters with a needle point. 
Here, finally, proof of elongation was secured. The millimeter 
spaces in the lower portion of the marked areas were found to be 
farther apart in the daily observations, though the elongation was 
slight ana continued only three days. The slight pushing up of the 
leaf from below showed that only the upper portion of the elongating 
area had been exposed. It seems probable that exposure to the air 
checked the elongation after three days, and that the severe cutting 
brought the whole growth to nearly the zero point. Subsequent 
experiments, where holes were bored to the center of the trunk, 
determined that this pushing up of tissues was quite active 18 inches 
below the bud crown, and at 2 feet below there was still a discernible 
action. This mode of growth is referred to as “basipetal” by Jost 
in the following paragraph: (-4) 
