Newcombe, Sensitive Life of Asparagus plumosus. 
19 
III. Thermotropic Relations. 
Inasmuch as subsequent study was to be made of the nutation 
of the shoots in the dark, and generally the method used to sucure 
darkness was by covering the experimental shoots with black paper 
cylinders or inverted cones, thus allowing the uncovered shoots of 
the same rhizomes to carry on their carbon-assimilation, it was 
desirable to see how sensitive the covered shoots might be to 
differences of temperature on opposite sides of the opaque paper 
coverings. In this study it soon became evident that it would be 
unsafe to allow direct sunlight to fall on the covers even for brief 
periods. Sometimes in 40 minutes, and nearly always in an hour, 
strong negative thermotropic curves resulted from the shining of 
the sun on the covering, even tho the tips of the shoots were 
several centimeters away from the paper cover. When these 
thermotropic curves were made, the temperature within the covers 
varied from 29° to 34°. 
IV. Development of Diageotropism. 
The following study enters into considerable detail of the 
development of diageotropism from negative geotropism in shoots 
from the seedling stage to the development of the twining con¬ 
dition, and hence deals with shoots up to an an age of one and 
one-half to two years, except seedlings. 
1. Heliotropism generally determines the plane of 
diageotropic curvature. If new shoots be allowed to come up 
from the rhizomes which already bear assimilating shoots, these 
growing shoots will be found, from the time they are 2 or 3 cm 
high, bending their tips from the vertical in response to the sun¬ 
light, making positive heliotropic curves from morning to night. 
Düring the night, the shoots erect their tips to the vertical Po¬ 
sition; and so this alternation of vertical with deflected direction 
goes on day and night tili the development of diageotropism fixes 
the tip in a definite line of a horizontal plane. It is thus the in- 
fiuence of light which usually determines the direction of the plane 
of curvature of the diageotropic tip. But the heliotropic Stimulus 
of light is not an absolute necessity to the taking of the horizontal 
Position. If a potted plant with a vertical orthotropic shoot be 
placed in the dark some days before ready to assume the horizontal 
Position, it takes this horizontal position in the absence of any 
heliotropic curve. But the plant in the dark offers gravitation, 
which causes the diageotropic* curve, a footing for attack by the 
frequent nutations which carry the stem-tip 10° to 20° from the 
vertical. 
2. Behavior of shoots never in light. The tests for this 
topic were carried out on shoots rising from rhizomes. In Order 
to determine more exactly the effect of light, shoots were used 
that were never, from the origin of the bud on the rhizome, ex- 
posed to light. To obtain such shoots, pots of plants were examined 
2 * 
