Sept. 1, 1925 
Thermostasy of Growth of the Date Palm 
447 
THE TEMPERATURE OF RESPIRATION 
Without means for definite determination, it must nevertheless be 
assumed that to the warming effect of the daily air maxima there 
should be added some amount of heat developed by the activity of 
the enormous bud, which comprises not only the region where new 
organs are in formation but also the basal zones of all leaves still in 
process of elongation, sometimes six or eight in number. Jost (9, 
p. 898-401) mentions “growing points” along with germinating seeds 
and inflorescences as exhibiting temperatures higher than that of the 
surrounding air, but lays special emphasis on the high temperatures 
observed in the inflorescences of Palmeae, Cycadaceae, Victoria regia, 
and Arum italicum . He adds in the supplement (10): “The heat 
produced is thus not a protection against frost.” 
MacDougal (14, p- 67) by inserting thin-bulbed thermometers “in 
the tissues of joints of cacti from which new shoots were arising” 
observed temperatures at times 8° or 9° C. above surrounding air. 
The writer is unable to find any record of such temperature tests of 
the buds or growth centers of palm trees. Of the comparative tem¬ 
peratures illustrated in the five figures previously referred to, the 
greatest actual difference between the growth center and the sur¬ 
rounding air was 28.8° F. at 6.10 a. m. on February 19 (Table I). 
For protection to the growing tissue this was most important, since 
in the adjacent garden buds of many deciduous fruit trees were 
destroyed by that freeze. This was at a time when the night leaf 
growth was only 3 mm., hence the cell activity and respiration must 
have been very slight and the generation of heat from this source 
negligible. 
The extent to which respiration becomes a factor in the interior 
temperature of the phyllophore may well be left to further experi¬ 
mentation. 
It has been shown in another line of experiments that the leaf 
elongation of the date palm is made in the night and that growth 
entirely ceases in direct sunlight. But it has also been demonstrated 
that by excluding all light from a date plant at midday, a rate of 
growth is quickly resumed similar to that of the night hours. This 
would involve the activity of the meristem cells of the growth center 
following a maximum of respiration. Any rise in temperature, con¬ 
trary to the usual downward direction of the temperature curve at this 
hour, could then be credited directly to the respiration in progress. 
With the aid of a recording auxanometer and a recording resistance 
thermometer, it should be possible to coordinate almost to a minute 
the resumption of the suspended growth with any rise in temperature. 
TEMPERATURE CONTROL OF THE GROWTH CENTER OF, ENDOGENS 
A survey of the literature on the temperature relations of plants 
fails to show recognition of the following four vital facts of plant 
physiology which are brought out in these studies of the date palm: 
(1) The existence in an important plant group of what may be 
termed “giant buds” or growth centers, within which are in progress 
simultaneously (and in the date palm, at least, perennially) the 
basal or intercalary growth of leaves and flower spathes, and the 
apical growth of the trunk. 
