220 



HEAT AND PROTOPLASM 



[Ch. VIII 



which molecular decomposition and synthesis occur, vary directly 

 with it. This is an important consideration in our study of pro- 

 toplasm, for most of its changes are chemical changes. 



A word should be said concerning general methods of apply- 

 ing heat to protoplasm. In the case of the higher plants and 



seedlings, the device of Sachs ('92, 

 p. 117) may be employed. This 

 consists of two metallic vessels, a 

 and i (Fig. 64), of similar form, 

 one placed inside of the other, the 

 interspace being 'filled with water. 

 Within the inner vessel is placed 

 the pot (i) with the object of ex- 

 perimentation. The whole is cov- 

 ered over by a half globe of glass 

 (^), extending down to below the 

 level of the top of the pot. The 

 water is heated by a lamp (Z) be- 

 low, by which means moisture and 

 warmth are carried to the plant. 



In the case of the lower organ- 

 isms, brief experiments may be con- 

 ducted in shallow aquaria for the 

 horizontal microscope (Fig. 65), like 

 those devised by Coki ('93). It is 

 preferable to put inside of the outer 

 vessel a smaller glass vessel, which 

 shall contain the organisms and 

 the thermometer marking the tem- 

 perature of the water. For long- 

 continued experiments where con- 

 stant high temperature is required, 

 a warm oven, such as is used in bacteriological work, is essential. 

 The production of extremely low temperatures offers special 

 difficulties. For temperatures to — 40° or so, various freezing 

 mixtures can be employed. Of these chopped ice and common 

 salt in equal parts give a temperature of — 18° ; calcium chlo- 

 ride and snow, in proportions of 3 to 2, give — 38°; and cal- 

 cium chloride and snow, in the proportion of 2 to 1, give — 42°, 



Fig. 64. — Apparatus for study- 

 ing the effect of heat upon 

 germination in phanerogams, 

 a, the external; i, the inter- 

 nal vessel, between which is 

 a water space ; t, flower-pot 

 filled with earth and con- 

 taining a seedling of maize 

 ■p ; A, three supports for the 

 glass hell g ; u, support for 

 the flower-pot ; d, tripodal 

 iron stand carrying the spirit- 

 lamp I. (From Sachs, '92.) 



