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 cnrves 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. 

 During 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 nsed 

 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 



