132 PHYSIOLOGY OF NUTRITION. 



perature of 60 C. Owing to the influence of the high tempera- 

 ture, the movement of the protoplasm is at once arrested, and is 

 not resumed with lapse of time. The leaf becomes disorganised, 

 and is in fact dead. 



Very many kinds of leaves (I have used, e.g., cabbage leaves) do 

 not change much in colour, when placed for a time in water at a 

 high temperature (e.g. 60 C.). The leaves, however, very quickly 

 die ; the cells lose their turgidity, and the leaves become flaccid. 

 Nor can they be restored to their normal turgescent condition. If 

 we immerse in hot water leaves whose cells are rich in acid (I 

 found leaves of Begonia manicata and Vitis vinifera very satis- 

 factory), they rapidly become discoloured, since the chlorophyll 

 grains, owing to the destruction of the protoplasm, are now brought 

 into direct contact with the acid cell-sap, and the acids decompose 

 the chlorophyll. If we lay Begonia leaves in water at a tempera- 

 ture of 55 C., they become discoloured in the course of two 

 minutes; in water at a temperature of 75 C., they lose their 

 green colour almost instantaneously. Microscopic examination of 

 tangential sections of killed leaves of Begonia manicata shows that 

 the chlorophyll granules are no longer green but brownish in 

 colour. 



That the protoplasm, in death brought on by exposure to too 

 high temperature, loses its normal constitution, and consequently 

 allows the acids of the cell-sap to traverse it easily by osmosis, we 

 can easily determine, according to my experience, as follows : A 

 piece of the petiole of a living Begonia manicata leaf is washed, 

 and laid in distilled water. A second piece of the same petiole is 

 killed by immersion in water at 60 C. When it has become dis- 

 coloured, we at once place it in distilled water. After a time we 

 remove the pieces of leaf, and add to the water in each case 

 Calcium chloride solution. That in which we laid the killed 

 piece of leaf becomes turbid, owing to separation of Calcium 

 oxalate ; the other remains clear. The disorganised protoplasm 

 has become permeable to the Oxalic acid of the cell-sap, and has 

 allowed it to pass out into the surrounding water. 



If hairs from the stamens of a- Tradescantia flower are killed 

 by immersion in water at 55 or 60 C., then mounted on a 

 slide in a drop of water, and examined under the microscope, it is 

 seen that the red or violet pigment of the cell-sap passes over into 

 the space between the protoplasm and the cell-wall, and ultimately 

 escapes from the cells into the surrounding water. The uninjured 



