224 TRANSLOCATION IN PLANTS 



be nearer than 6°C. Temperatures somewhat above 6°C. 

 had no significant effects on transport. Comparable effects 

 on regeneration were reported by Child and Bellamy (1919). 

 Although the data are not sufficiently complete to demon- 

 strate just how abrupt the stoppage is or what the critical 

 temperature is, yet they show very clearly that the influence 

 of a fall of a few degrees at the lower range, somewhere 

 around 4 to 6°C., is much greater than a similar fall in 

 temperature at a higher range, such as between 10 and 

 25°C. It seems probable that the critical temperature will 

 vary with the plant, its previous condition, and the time 

 of exposure. This would follow if, as seems to me probable, 

 the stoppage is related to stoppage of protoplasmic stream- 

 ing. Ewart (1903) has observed protoplasmic streaming 

 to cease when lowered to a few degrees above zero and then 

 later begin again at the same temperature. 



Kruseman (1931), though he found some retardation 

 especially at the lower temperatures when he cooled the 

 petioles of Phaseolus leaves, did not find the marked 

 retardation that I did and disagrees with my interpre- 

 tation. Most of the temperatures he used, however, were 

 5°C. or above, which is so near the critical temperature 

 that streaming may not have been stopped all the time. 

 Even though his temperatures remained fairly constant, 

 in several instances the temperature rose for varying 

 periods above the average temperature given. In my 

 experiments a maximum-minimum thermometer placed in 

 the line showed in most experiments a smaller range, a 

 maximum of 4°C. and a minimum of 3°C. for the data 

 reported in Table 24. He suggests that experimental 

 errors in my method of using paired leaves may have 

 accounted for the differences obtained. However, the 

 differences were so great, the findings were so consistent 

 with different individuals and in different experiments, and 

 the statistical treatment showed such striking odds, that 

 I am convinced the data are really significant. Stanescu 

 (1933) obtained data indicating some retardation, but these 

 effects also were much less pronounced than my own. 



