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Journal of Agricultural Research 
Vol. XXXI, No. 5 
(2) Stabilized temperatures within this growth center, with 
a decided gradient between them and those of the surrounding air, 
higher or lower, as the case may be. 
(3) An insulating zone of tissues of low conductivity, surround¬ 
ing the growth center, and resisting the penetration of air tempera¬ 
tures from without and the escape of heat from within; a stabilizer. 
(4) The stabilizing influence of the ascending sap current, tending 
to hold the growth center temperatures within a few degrees of the 
temperatures of the soil penetrated by the plant roots. 
Pfeffer C 19 , pp. 879 , 881) appears to have had an understanding 
of the influence of the ascending sap current in exogenous trees. 
Rameaux (20) recognized the influence of “organic action” as 
“vital heat” in the plant, but attributed the plant temperature 
chiefly to “the influence of the climate, acting in two different 
manners—(1) directly upon the plant organs exposed to the at¬ 
mosphere; (2) upon the soil and consequently upon the sap drawn 
up by the plants.” 
The direct action of the sun’s rays was considered the strongest 
influence in governing plant temperatures and he recognized the 
effect of the slow penetration of the heat through the badly con¬ 
ducting wood. 
Thus the alternations of the day’s heat and the night’s coolness 
did not reach the center of the trunk of 0.5 meter diameter until 
after a lag of 15 hours, or even 24 hours. 
However, with the exogenous trees which were under observation, 
such temperature phenomena could have had little stabilizing in¬ 
fluence on the meristematic tissues and none is claimed by this 
author; for he records that “during the warmest days of April, a 
branch of a poplar, 4 cm. thick, showed in the central strata a 
temperature at noon which was 8°, 10°, or even 13° C. higher than 
the surrounding temperature. ” 
Of the influence of the sap current, Rameaux says: “ The ascend¬ 
ing sap increases or diminishes the temperature of the parts which 
it traverses according as these parts possess a temperature lower 
or higher than that of the sap itself. ” 
Much importance is attached bv this author to the transpiration 
rate of the foliage in enhancing the flow of sap through the trunk 
and branches and so increasing its cooling power as it meets the 
heat penetrating from the surface. In support of this idea he sub¬ 
mits a table of the interior temperatures recorded in two trees; in 
the first period, growing normally, the temperatures of the two trees 
during various hours oi the day compared very closely. During the 
second period, with the second tree dead and presumably not trans¬ 
piring and without the ascending sap current, the dead tree showed 
during the afternoon temperatures of from 7° to 10° higher than 
those of the normal tree cooled by the ascending sap. In the third 
period, with tree No. 1 shorn of all its top, hence with no ascend¬ 
ing sap current, its interior temperature compared closely with 
that of the dead tree. 
De Candolle (A. P.) 7 (6) Physiologie Vegetale, is cited frequently 
by both Pfeffer and Rameaux. De Candolle recognized the impor- 
7 Citations from DeCandoUe, Aug. Pyr., (6) in Physiologie V6g6taJe; (p. 879) Schoepff (2) Naturforscher, 
23 sti., p. 1-37. Halle, 1788; (p. 880) Hermstaedt (2), Mag. a. GeseUsch. naturf.freunde in Berlin , 1808, p. 316; 
(p. 879) J. Hunter, (1) Philos, trans. for 1775 et 1778; Journ. de phys., 9, p. 294; 18, p. 12 et 216. 
