464 



EFFECT OF HEAT 



[Cn. XVIII 



klinostat whose axis of rotation is parallel to the window, and 

 are subjected to rays of heat from a warmed plate of iron held 

 in the axis of rotation, they turn with reference to the source 

 of heat. Thus WORTMANN found that, at a distance from 

 the iron plate of 10 cm., corresponding to a temperature of 

 27 C., all the spore-bearing hyphse of Phycomyces turned in 

 seven hours from the source of heat; they were negatively 

 thermotropic. Under the same conditions the plumule of a 

 seedling maize was positively thermotropic. The roots of the 

 hyacinth when growing in water turn towards the adjacent 

 stove-pipe. The flower-buds of Magnolia turn, in the field, 

 from the dark heat-rays of the sun (VOCHTING). 



2. Conducted Heat. The methods employed in working with 

 this agent have been as follows : WORTMANN used a box 

 divided into two compartments by a diathermous partition. 

 Through one compartment there passed a constant current of 

 cold water ; the second was filled with sawdust in which seeds 

 were imbedded. In front of this second compartment, on the 

 opposite side from the cold-water chamber, was a gas flame, the 

 source of energy. The seeds were scattered through the saw- 

 dust, so that some were nearer the flame, others nearer the 

 cold hinder wall. The temperature of the sawdust near each 

 seedling was determined. KLERCKER used essentially the same 

 apparatus, excepting that a box of hot water replaced the flame. 



The results of the experiments are summarized in 



TABLE LV 



SHOWING FOR THE RADICLES OF SEEDLINGS OF VARIOUS SPECIES THE RELATION 

 BETWEEN THE TEMPERATURE AND THE SENSE OF THERMOTROPIC RESPONSE 



