iQ2o] CHILD &• BELLAMY— BRYOPHYLLUM 253 



As regards the third type of physiological isolation, by the 

 blocking of passage of the action or effect, whatever its nature, less 

 is known. McCallum (21) obtained some results along this 

 line in plants by means of local anaesthesia, and it is a familiar 

 fact that the passage of the nerve impulse can be blocked by an 

 anaesthetized or a cooled region, as well as by various other means. 

 For a long time one of us has had in mind experimentation along 

 this line with plants, and Loeb's (14-20) recent work on Bryophyl- 

 lum constituted an additional stimulus. Finally, in 1918-1919, 

 experimentation was begun in the attempt to determine whether 

 physiological isolation could be brought about by a local reversible 

 action on some part of the connecting path between dominant and 

 subordinate parts. Since it seemed desirable to avoid the use of 

 anaesthetics or other chemical agents which might enter the plant 

 tissues and be transported in one direction or another, low tern- 

 perature was used as the blocking factor. 



Method and apparatus 



The low temperature was obtained by a current of cold water 

 flowing through a block tin pipe of ^ or T f inch inside diameter, 

 this pipe being bent into loops or coils of the proper diameter 

 and length to surround the portion of the plant to be cooled. In 

 this way various lengths of stem, from 1 cm. to a whole inter node 

 or more, could be cooled. In preparation of the plant, the region 

 to be subjected to the low temperature was first wrapped in tin- 

 foil, and the loop or coil of pipe, supported by clamps attached 



* 



to ring stands, was fitted about it in such manner that it was not 

 in direct contact with the plant at any point, the space between 

 stem and pipe being usually o . 5-1 cm. This space was then packed 

 lightly with moistened absorbent cotton to keep the temperature 

 as constant as possible, and finally the whole coil was wrapped 

 closely in non-absorbent cotton to protect it from the outside 

 temperature. In many experiments a thermometer was also 

 inserted in the coil, but it was found that so long as the tempera- 

 ture of the water passing through the coil remained constant there 

 was practically no change inside. In a part of the experiments 

 the temperature of the water used was maintained in a tank by 



