68 PENHALLOW ON MECHANISM 
CONCLUSION. 
We may now proceed to sum up the conclusions which the foregoing facts appear to 
justify. 
TEMPERATURE.—The observations here recorded are in harmony with the views 
generally held, that within certain limits and conditions, otherwise favorable, higher 
temperatures induce more rapid growth. According tothe experiments of Sachs upon the 
germinating seeds of Cucurbita, the most rapid growth occurred under the influence of a 
temperature of 33.7° C.; the condition, doubtless, being such that the normal tension of 
parts was fully maintained throughout, or subject to but slight variations. In our own 
observations, the greatest growth, as represented in tendril movement, occurred under a 
temperature of 24.4°C.; while the most rapid growth of the vine occurred when the 
temperature ranged from 29° C. to 36.6°. It is important, however, not to lose sight of the 
fact that in these cases, there were important modifying influences which would affect 
growth through the normal tension of the tissues,—a disturbance of which frequently 
occurs as a result of high temperatures. The general effect of temperature becomes 
conspicuous at once, if we compare the growth for an even number of hours when the 
temperature is above 30° C., with growth for the same period when the thermal range is 
from 25° C. to 30°. We shall then find the growth in the latter case to be greater, as the 
following table will show :— 



Number of Average ae Average Growth = ve 
Observations. Temperature. | Total Growth. | per hour. Relative Humidity. 
6 27.0° C. 2.0 in. 0.333 in. Relatively great. 
6 34.9° 1.6 in. | 0.266 in. Relatively small. 






The relative humidity of the atmosphere, or the degree of saturation dependent upon 
temperature, exerts a direct influence upon conditions of tension in growing parts, and 
consequently upon growth itself, by inducing more or less rapid transpiration. Excessive 
humidity is consistent with more rapid growth. We may, therefore, reaffirm the already 
accepted principle that increasing temperature promotes growth, so long as it does not 
disturb the normal conditions of tension. 
Licur.—Alternations of day and night cause a marked influence upon and variations 
in the phenomena of growth. Light is generally accepted as exerting a retarding influ- 
fluence upon growth,' and other conditions being equal, we should naturally expect to find 
the greatest elongation of the axis and most rapid movement of motile parts during the 
hours between sunset and sunrise. 
From the experiments now under consideration, we find that the growth during 
hours of darkness was in reality less than that during an equal number of hours of 


1 Sachs’ Text-book, 755. 

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