220 



HEAT AND PROTOPLASM 



[Cn. 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 () 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 (T) 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 CORI ('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, 



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 ; h, three supports for the 

 glass bell g ; u, support for 

 the flower-pot ; d, tripodal 

 iron stand carrying the spirit- 

 lamp /. (From SACHS, '92.) 



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 33 ; and cal- 

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



