RELATIONS OP PROTOPLASM TO HEAT. 203 



enough to receive the body of the microscope. Through a hole 

 in the top of the box the tube of the microscope projects for a 

 short distance, and the front of the box is furnished with a glass 

 window, which affords enough light for the mirror. The space 

 between the walls of the box having been filled with water, and 

 the object placed on the stage of the microscope, a lamp under 

 the box is lighted, and the effects of the increase of temperature 

 noted. It is best in this case to have the thermometer in the 

 closest proximity to the slide. It is essential in the use of both 

 these instruments to note the temperature at short intervals, 

 and it is only by the greatest care in the use of the thermometer 

 that an3' trustworthj- results can be obtained (see Fig. 170). 



559. As might be expected from the nature of heat as a mode 

 of molecular motion, the rate of protoplasmic movement is 

 accelerated hy increase of temperature up to a given point (the 

 optimum) ; with increase beyond this point the movement may 

 continue, but with diminished rapiditj', until an upper limit of 

 temperature (the maximum) is reached, above which no move- 

 ment is observable. At or verj' near this limit structural changes 

 take place, and death of the protoplasm speedilj' ensues. 



560. The optimum temperature for protoplasmic movement 

 is different for different plants, but is not far from 37°. 5 C. 



Name of plant. Optimum temperature. Observer. 



jSfitella syncarpa 37° Nageli.i 



Chara foetida 38°. 1 Velten.^ 



Vallisueria spiralis 38°. 75 "2 



" " 40° Sachs.''! 



Anacharis Canadensis . . . 36°. 25 ... . Velten.^ 



561. The maximum temperature beyond which no movement 

 is seen, is also different for different plants, but may be given as 

 not higlier than 50° C. 



Name of plant. Maximum. Observer. 



Chara fcetlda 42°. 81 Velten.''' 



Vallisneria spiralis 45° "2 



" 60° Sachs.s 



Sachs * states that when the hairs of Cucurbita Pepo are im- 

 mersed in water of 46° or 47° C. the protoplasmic movements 

 are arrested within two minutes ; but that the hairs can bear 



1 Beitrage z. wiss. Botanik, 1860, ii. p. 77. 



2 Flora, 1876, p. 177 et seg. 

 s Flora, 1864, p. 5 et scq. 



* Lehrbuch der Botanik, 1874, p. 700. 



