[Vol. 2 



536 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



VI. Effects of High and Low Temperatures 



After the preliminary experiments noted above on the effect 

 of heat had been carried out it was desired to study the ques- 

 tion further and determine the resulting exosmosis curves at 

 the extreme temperatures, high and low. The preliminary ex- 

 periments had involved temperatures requiring a considerable 



time interval to produce positive results. The data now to be 

 presented concern temperatures sufficient in themselves to ef- 

 fect decided injury in a very short period. By varying the 

 time factor, therefore, results could readily be obtained on 

 both sides of the point of injury. 



For the experiment, the results of which are plotted in fig. 7, 

 cultures were set out of doors for the time indicated, directly 

 exposed to the winter temperature. The tops showed some 

 signs of freezing after a few moments, but the effects did not 

 become noticeably worse until the cultures were brought in- 

 side, when all the plants in each culture immediately drooped 

 over the wire supports and became entirely limp, and soon 

 died. The tops did not yellow, but retained the green color 

 after death. Except for the root tips of the plants in No. 3, 

 which were slightly brown at the end of 5 days, all the roots 

 of the treated plants remained turgid, white, normal, and in 

 healthy condition. This is interesting in view of the fact that 

 while no ice was formed in No. 1, there was a slight fringe of 

 it between the water and the tumbler in No. 2, and a hollow 

 cylinder of ice one-fourth inch thick formed next to the 

 tumbler wall in No. 3. In the last-mentioned culture there was 

 also a film of ice over the surface of the water and the roots 

 were frozen to the ice mass so that on lifting the plants from 

 the tumbler the mass of ice adhered to the roots. The first 

 readings were taken only after the ice had melted. The tem- 

 perature at first was — 6°C. but by the end of the first hour 

 it had risen to — 2°C, where it remained practically con- 

 stant for the balance of the interval. 



At a temperature of — 6.5° C. it is seen by reference to fig. 8 

 that while for exposures of the plants alone (the roots being 

 out of the water) of 2 and 3 minutes, marked exosmosis imme- 



