THE INFLUENCE OF TEMPERATURE 



When experiments are performed in water whose temperature is 

 altered, as were those of Velten, lower optima and maxima are always 

 obtained than when the objects are heated in moist air. This is in part 

 due to the greater rapidity with which they gain the required temperature 

 in the former case, although the deficiency in the supply of oxygen aids 

 in prolonged exposures to lower the cardinal points. In any case, it is not 

 easy to see how it was that Nageli found streaming to increase in rapidity 

 in the cells of Nitella syncarpa up to 37 C., when it suddenly ceased, 

 unless the temperature was raised so rapidly as to exercise a shock- 

 effect 1 . The existence of an optimum temperature is always shown more 

 or less clearly 2 , especially when the exposure is prolonged, although 



FlG. 52. Combined hot stage and gas-chamber. The three apertures lead to tubes projecting externally, and 

 are used to ensure the better diffusion of dense gases. Through the upper aperture electrodes insulated at their 

 bases may be inserted. (After Ewart.) 



Schafer's 3 attempt to give the detailed progress of the curve is largely 

 futile owing to its variable character. 



The zoospores of those Algae which grow at Spitzbergen at o C. to 

 i -8 C. are presumably motile at this temperature. The zoospores of 

 Vaucheria clavata 4 , Ulothrix zonata 5 , and Haematococcus lacustris 8 are in 

 fact motile in water at o C., whereas those of Botrydium granulatum 7 fall 

 into cold rigor at 6 C. According to Strasburger, the optimum for the 

 zoospores of Haematococcus lacustris lies between 30 and 40 C., the 



1 Nageli, Beitr. z. wiss. Bot., 1860, Heft ii, p. 77. Cf. Velten, Flora, 1876, p. 177. 



* Schultze, Das Protoplasma d. Rhizopoden u. Pflanzenzellen, 1863, p. 48; Sachs, Flora, 1864, 

 p. 65 ; Hofmeister, Pflanzenzelle, 1867, pp. 47, 53 ; Wigand, Botanische Hefte, 1885, I, p. 216; 

 Klemm, 1. c., p. 635. For observations on streaming in the plasmodia of Myxomycetes see Kiihne, 

 Unters. ii. d. Protoplasma, 1864, pp. 47, 53. 



8 Schaefer, Flora, 1898, p. 135. Cf. Ewart, On the Physics and Physiology of Protoplasmic 

 Streaming in Plants, 1903, p. 59. 



* Unger, Die Pflanze im Momente d. Thierwerdung, 1843, p. 57. 



* Dodel, Jahrb. f. wiss. Bot., 1876, Bd. x, p. 484. 



6 Strasburger, Wirkung d. Lichts u. d. Warme auf Schwarmsporen, 1878, p. 62. 



7 Strasburger, 1. c. 



