EFFECT OF SUDDEN CHANGES OF TEMPERATURE 67 



10 or 15 C. to 45 C. The intensity of the stimulus is proportional to the 

 rapidity of the change, and hence a rise of 25 or 30 C. suffices to produce 

 a temporary stoppage of streaming without any injurious after-effect in the 

 above plants, and also in Elodea^ Vallisneria, and Tradescantia if cells are 

 suddenly transferred from cold (ioC.) to hot (35 C. to 40 C.) water. 



A similar shock-effect is produced when a streaming cell is suddenly 

 subjected to a low temperature. Thus Kuhne 1 found that when hairs of 

 Tradescantia were cooled to 14 C. in five minutes, streaming ceased and 

 the protoplasm separated into globules, but became normal again within 

 ten minutes at room-temperature. Similar results were obtained by 

 Hofmeister with an exposure of ten minutes to 8 C., and by Klemm 2 on 

 subjecting cells of Char a and hairs of Momordica and Trianea to tem- 

 peratures of 5 C. to 6 C. for ten minutes. In the older experiments the 

 registered temperature was probably lower than that to which the plants 

 were actually exposed, but even Klemm's observations form no sure proof 

 of a shock-effect, for the temperatures given are below the minimal points 

 for prolonged streaming in these plants, and they are all killed by being 

 frozen at these temperatures 3 . Satisfactory proof was, however, easily 

 obtained in the following manner: Cells of Chara, Nitella, &c., were 

 enclosed in fine capillary glass tubes partly filled with water, which were 

 plunged into a freezing-mixture of snow and salt for from twenty seconds 

 to two minutes. The tubes were immediately placed on the microscope 

 stage and examined, when it could often be seen that streaming is at first 

 present, but then suddenly temporarily ceases, as the result of the after- 

 effect of the shock of cooling. Rapid examination is required, since the 

 latent period of stimulation is rarely as much as ten seconds. Hence 

 a better mode of experimentation is to place the capillary tube within a 

 large flattened one which rests on the microscope stage, and through 

 which cooled brine can be passed 4 . 



Staminal hairs of Tradescantia^ root-hairs of Trianea, and leaf-cells of 

 Chara and Nitella,'\i lowered from ioC. to zC. in five to ten minutes, still 

 show slow streaming, which is progressively retarded and ceases in one to 

 a few hours. If the preparations are brought to 15 C. immediately on 

 cessation, streaming is actively resumed after twenty minutes. Longer 

 exposure, if not fatal, prolongs the latent period of recovery slightly. The 

 immediate decrease of velocity is largely due to the increased viscosity of 

 the protoplasm at low temperatures, but the subsequent steady fall is 



1 Unters. iiber das Protoplasma, 1864, p. 101. 



2 Hofmeister, Zelle, p. 54 ; Klemm, 1. c., p. 16. 



Cf. Ewart, Ann. of Bot., Vol. XH, 1898, pp. 365-6. 



* The rapid condensation of water upon the cold tube is apt to be troublesome, but it can almost 

 entirely 6e avoided by directing a jet of dried air upon the outside of the tube just beneath the 

 objective. 



F 2 



