14 



Göte Turesson 



Pot cultures of these plants were placed in a phototropic chamber for six hours. 

 The branches showed the following deviations from the original angle with the 

 horizon at the end of this time (Table II). 



Table II. 





Original 

 position 



Final 

 position 



Deviation 



1 



A. pat. ercctuni 



98 



70 



+ 28 



2 





93 



79 



+ 14 



3 



» » ï- 



57 



21 



+ 36 



4 





34 



4 



+ 30 



5 



A. prostratum Bough. ... 



60 



40 



+ 20 



6 





77 



50 



+ 27 



The branches were now all turned against the small opening in the box facing 

 the bright sun, and remained there while illuminated. Thus, these plants are plainly 

 positively heliotropic even in strong sunlight, and the supposition that the pla- 

 giotropy is due to negative heliotropisni becomes very doubtful. We are thus com- 

 pelled to admit that hydrotropic, thermotropic, and heliotropic factors cannot be the- 

 agents calling forth the peculiar prostrate habit in the above-mentioned plants. 

 There remains geotropism. 



If shore plants which in the open have the above-ground organs more or 

 less horizontally expanded are transplanted and put in weak light or still better in 

 a dark room it is found that the stems and leaves (in the case of rosette-plants) 

 rise and take up a vertical position within a short time. This property is illustrated 

 in Table III, where some data have been brought together. The plants were kept 

 in the dark room from July 5— July 11. Two pairs of branches on the chief axis 

 have been investigated, one upper and one lower, and two angles have been 

 measured on each. The upper angle is the one formed by the uppermost inter- 

 node of the lateral branch with the horizon, the lower angle is that formed by 

 the very base of the lateral branch with the chief axis. In the case of Leontodon 

 autumnalis the number of degrees has reference to the angle formed by the basal 

 part of the scape with the perpendicular. 



