THE INFLUENCE OF TEMPERATURE 



59 



probably acts as a physical stimulus and not as a chemical one, such as is 

 exercised by many dilute solutions, for when cells are completely immersed 

 in i to 3 per cent, cane-sugar solution, a nearly constant retarding action 

 seems to be exercised. 



SECTION 25. The Influence of Temperature. 



In 1774 Corti stated that streaming returned to cells of Char a which 

 had been frozen at -5 C. and then thawed, but Dutrochet l found that the 

 minimum temperature for streaming in Chara was -1 C., and, as a matter 

 of fact, vegetating cells of Chara are killed by freezing at -5 C. Dutrochet 

 also found that in cells of Chara placed in water at 34 to 40 C. 

 streaming at first slowed, but subsequently became more rapid, whereas at 

 45 C. it soon permanently ceased. The first slowing is, however, merely 

 a shock effect, and if the rise of temperature is not too rapid, a continuous 

 increase is shown up to, or even above, the permanent optimum tem- 

 perature. The cardinal points obtained by different investigators are given 

 beneath. 



Sachs states (1. c., p. 39) that heat-rigor and cold-rigor may sometimes 

 be prolonged for hours without permanent injury, and has also shown that 

 the resistance to extremes of temperature is greater when in air than when 

 immersed in water. 



Velten 3 found that the increases in velocity become greater and 

 greater for each degree as the temperature rises from the minimum to the 

 optimum, and states that at each temperature a corresponding velocity is 

 immediately assumed, which undergoes no subsequent change. This latter 

 statement is entirely misleading, but the former one is supported by 

 Schaefer's calculation from Nageli's results that the direct response to rises 

 of temperature increases very nearly in geometric proportion to rises of 

 temperature between 10 C. and 30 C.* According to Hauptfleisch, rapid 

 rises or falls of temperature may induce streaming wherever a tendency to 



1 Ann. sci. nat., 1838, p. 25. 



2 Dutrochet, I.e., pp. 25-7 ; Memoires, 1837, ' P- S^ 1 \ Sachs, Flora, 1863-4, P- 39 '> Cohn, 

 Bot. Zeitg., 1871, p. 723 ; Velten, Flora, 1876. 



3 Flora, 1876, pp. 210, 214. 



* Schaefer, Reaktion des Protoplasmas auf thermische Reize, Flora, 1898, Vol. LXXV, p. 135. 



