22 Macfarlane. — Contributions to the History of 



stated that Darwin's observations, as quoted above, had been 

 verified by the writer some months before, and that com- 

 parison of the minute structure of the leaves then used with 

 fresh leaves, and others preserved in various media had con- 

 vinced him that immersion for even a second or two in boiling 

 water causes coagulation of the protoplasmic substance and 

 disorganization of the starch that is so abundantly present in 

 many of the leaf cells. With one exception all of the leaves 

 closed within from two to five seconds after application of 

 the first few drops. The exception proved to be an interesting 

 one, and such as one might scarcely have hoped to obtain. 

 The leaf was rather small — about half the usual size — and 

 like the others, began to close shortly after a few drops of 

 the boiling water had been let fall on the upper surface, but 

 just as it had half closed, movement stopped for an instant, 

 and it then slightly relaxed to retain the heat-stiffened position 

 for the remaining half hour, during which the plants were 

 under observation. 



As regards after-effects the last mentioned leaf was the 

 only one which showed speedy and pronounced death changes, 

 for next clay it had a yellow flaccid aspect and in three days 

 was dry, brown, and shrivelled. The other leaves of the same 

 series retained their green appearance for nearly a week, 

 except for an area about one-eighth to one-quarter inch across, 

 marking where the water had been first applied and which soon 

 became yellow and then brown. All of these leaves gradu- 

 ally became yellow, and in a fortnight were dead. Four 

 of those acted on at from 50 to 75 C re-expanded, but as the 

 individual leaves had not been marked in relation to water 

 temperature we are unable to say which persisted. 



The above facts prove that a gradual increase in tempera- 

 ture produces quickened stimulation up to a point where the 

 contractile protoplasm and food materials are so affected that 

 disorganization and death ensue. But the subsequent fate of 

 most of the leaves points to a permanent injury, either local or 

 general, to the living cell contents. 



Six leaves were selected on two plants standing in a room 

 with a temperature at 72 F. Small pieces of ice were care- 



