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 (?) 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- 

 FIG. 04. Apparatus for study- ducted in shallow aquaria for the 



ing the effect of heat upon horizontal m i croscO pe (Fig. 65), like 



germination in phanerogams. /-^ 



a, the external; i, the inter- those devised by CORT ( 93). It is 



nai vessel, between which is preferable to put inside of the outer 



a water space; t, flower-pot ,, 1-1 



tilled with earth and con- vessel a Smaller g laSS V6SSe1 ' which 



taining a seedling of maize shall contain the organisms and 



p ; h, three supports for the the thermometer marking the tem- 



glass bell y ; u, support for 



the flower-pot; d, tripodal perature of the Water. tor long- 

 iron stand carrying the spirit- continued experiments where con- 

 lamp I. (From SACHS, '92.) 1-1 j 



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 -- 33; and cal- 

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



