428 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
The growth characters of the date palm may be summarized thus: 
In the seedling a bulb-like stem pushes up from its growth center by 
basal increment centripetal spirals of pinnate leaves which make no 
elongation after they emerge. From the rounded base of this stem 
is produced an increasing number of cordlike roots which may ulti¬ 
mately reach the thickness of a finger and extend over a radius of 
30 to 40 feet or more. They have only small lateral branches and 
feeding rootlets without root hairs. These roots must convey a 
large volume of water to the trunk, and at the same time are so 
P rovided with fiber bundles that they can support the increasing 
eight of the trunk against the pressure of the wind. 
While there is a rapidly increasing production of leaves from the 
crown until normal development is reached, trunk growth for the 
first few years is mostly absorbed in increasing the diameter to the 
size characteristic of the variety, usually from 20 to 30 inches. As 
the tree advances in height this diameter increment is in progress 
over a considerable region, so there is always an apical “cone of 
growth” of varying lengths in different varieties, usually 3 or 4 feet, 
within which tissue building goes on. 
Unlike the old wood or duramen of an exogenous tree in which 
the sap channels soon become filled up and unable to convey the 
upward current, the vessels of the date palm trunk remain open and 
able to convey a strong flow of sap to the crown of transpiring leaves 
throughout the long life of the tree. 
The apical portion of the phyllophore is in a continuous state of 
subdivision into leaves, which are at the same time pushed to the 
outside by basipetal elongation and by the upward growth of the 
central axis. The new leaves are provided with fiber bundles, appar¬ 
ently by the branching of the bundles from below, the main axis 
continuing in the vertical direction. 
We must conceive of growth of the bundles taking place something 
as in the diagram (fig. 4). The basal portion of the leaves remains 
in a state of cell division and elongation for many weeks, while the 
blade as it emerges to the light quickly develops chlorophyll and 
takes on the characters of permanent or somatic tissues, able to 
endure the vicissitudes of its surroundings. There is soon established 
also a differentiation between the leaf tissue and bole or trunk tissue, 
for while date palm leaves usually retain this attachment to the 
trunk for a long time, a cross section at any time 2 or 3 feet below 
the top of the bud shows a well marked difference in structure 
between the leaf tissue and the trunk tissue. In the physiological 
action described in this paper a clear distinction must be kept in 
mind between (1) the protecting envelope comprising the broad 
bases of the midrib, with the enveloping sheaths, and (2) the trunk 
proper. These are shown admirably in Plate 3, a cross section of the 
same palm shown in Plates 4 and 5, at 2 feet above the ground. 
There has been much speculation in earlier periods as to the mode 
of growth and of the development of the fibro-vascular bundles in 
palms and other plants of the monocotyledonous class, which led to 
the preparation of papers by Desfontaines, Hugo de Mohl, and other 
botanists in the latter part of the eighteenth and the early years of 
the nineteenth century; and in 1839 Mirbel was sent to Algeria by 
the French Academy of Sciences to study palms in detail. Several 
of his papers appear in the volumes of Comptes Rendus in 1843-44 
