402 True. — Sudden Changes of Turgor. 
on the length of time of exposure to this temperature. The 
depression is regarded as the irritable response to the stimulus 
furnished by the exposure to the low temperature followed by 
the sudden change to the higher degree. The duration of 
the depression may be increased by lowering the minimum 
temperature-limit and by lengthening the period of exposure. 
An exposure to the lower temperature for less than a certain 
period of time is followed by no noticeable depression. 
Changes of temperature between i8° and 30° C. as extremes 
seem to be followed by turgor-changes only. That no 
momentary depression of the growth-rate takes place is hardly 
to be asserted. Indeed, it is likely that such takes place, but 
by reason of the slightness of amplitude becomes lost in the 
more striking spontaneous changes. It is also to be borne in 
mind that a slight uncontrolled interval follows the change of 
temperature. That in this interval a slight effect might have 
escaped observation is also not out of the question. 
In conclusion, I wish to express my sincere gratitude to 
Professor Pfeffer, and to his assistants, especially to Dr. Paul 
Klemm, for many kind suggestions and helpful criticisms; also 
for free access to the rich resources of the Institute. 
Botanical Institute, Leipsic, 
December , 1894 . 
