64 MICHIGAN ACADEMY OF SCIENCE. 



tion upward in some, downward or diagonally in others, I found tbat 

 the growing tip almost invariably struck out on a horizontal plane, 

 sometimes reAersing the upward turned side, again going through a 

 slight torsion to turn the flank uppermost. A plant with all of its 

 stems and branches approaching maturity but still growing slowly, 

 was inverted and suspended from a rafter in the greenhouse with all 

 sides about equally illuminated. After two days neither stem nor 

 branches showed the slightest change but all parts continued to grow 

 with their morphological upper side turned downward. After another 

 plant with two young erect shoots was likewise inverted, the stems soon 

 began to seek the horizontal plane but in oxjposite directions. In this 

 condition the plant was placed on the klinostat in a south window and 

 revolved on a horizontal axis for fifty-three hours. Neither of the shoots 

 took a wholly horizontal position but inclined to one side. A plant with 

 two younger and erect shoots was placed on the klinostat with practi- 

 cally the same conditions and results. The inclination was away from 

 the older stems of the plant in both cases. In turning, the young stems 

 were shaded by the older ones at the lower side of the circle while at 

 the upper side, they responded positively to the light. This points to 

 the conclusion that there is considerable sensitiveness to the light factor 

 at the early stage. 



To further prove the influence of light, the same plant was given 

 one-sided illumination in a black lined box and turned on its side with 

 the stems lying parallel to the window. In twenty-four hours the curva- 

 ture toward the lighted side was very pronounced, one stem having 

 passed through an angle of nearly ninety degrees to direct itself toward 

 the light, while to reach the horizontal plane, it would have had to drop 

 but forty-flve degrees. 



A plant whose stems had established their horizontal position and 

 developed primary, secondary, and tertiary branches, stood erect in 

 one-sided illumination for several days but all parts remained un- 

 changed. It is probable that vigorous growth had ceased and ability 

 to respond to the light had diminished. 



During a period of eight days attention was given to five young shoots 

 which grew in this time from 1 cm. to 13 and 15 cm. high. When the 

 plant was placed at an angle of forty-flve degrees, the stems through 

 negative geotropism bent and took the vertical position but the grow- 

 ing tips were all positively heliotropic. In various changes of position 

 the same results were noted. After branches had begun to develop 

 the stems became less responsive to the light. The young branches 

 were somewhat positively heliotropic, though in a less degree than a 

 growing stem. 



A thrifty plant with a growing shoot about six inches above the 

 earth was revolved on a horizontal axis for two and a half days in a 

 darkened chamber. Gravitation was evidently neutralized and no other 

 external force being present, the shoot continued to grow in a straight 

 horizontal line. On the other hand the shoot of a plant left in a sta- 

 tionary erect position in a dark room took the curve, i. e., responded 

 to transverse geotropism. From these experiments and other observa- 

 tions, I believe that in equally diffused light a shoot which naturally 

 grows from the plant at a small angle will make the diageotropic curve 

 in that direction toward which it is inclined, but when given one-sided 



