450 THE ANATOMY OF WOODY PLANTS 



photographic supply store. Whatever nitrocellulose is used, it 

 must be first washed in clean water and then carefully dried. The 

 stock should always be kept under water both to delay changes in 

 chemical composition which result in insolubility and to avoid 

 the risk of explosion. The dry nitrocellulose is dissolved in a 

 mixture of equal parts of good ether and absolute methyl or ethyl 

 alcohol. The first is more advantageous because it forms a better 

 solvent of the nitro-body. A number of solutions grading from 

 2 to 1 6 per cent must ordinarily be prepared and kept in labeled 

 bottles with wide mouths and good corks. As a preliminary to 

 imbedding, the material is freed of all gases which may have gath- 

 ered in its intercellular spaces as the result of the treatment with 

 hydrofluoric acid by means of the air pump. It is then freed of 

 water by two or three successive changes of absolute alcohol. This 

 reagent is best purchased in gallon bottles from a reliable manu- 

 facturer, since in containers of one pound capacity it is extremely 

 expensive in the United States. The dehydrated material is now 

 ready for infiltration with nitrocellulose. Small strong bottles are 

 prepared by twisting tough wire about their necks in such a manner 

 as to provide two short and diametrically opposite loops. The 

 wire used for this purpose should be tenacious and not too slender. 

 The bottles must have rather wide mouths and be stopped with 

 corks of the very best quality. One of the bottles prepared as 

 described is partially filled with nitrocellulose of the 2 per cent 

 strength, and the objects are dropped quickly into it from the 

 absolute alcohol so as not to absorb either air or moisture. There 

 should be some space intervening between the cork and the solu- 

 tion of nitrocellulose to allow for expansion in heating. The cork 

 is finally forced in and a piece of soft tough brass or copper wire is 

 passed through the loops on the sides of the neck of the bottle de- 

 scribed above. The wire is then drawn tight with the fingers or a pair 

 of pliers and twisted over the top of the cork so as to be held securely 

 in place even when the bottle is exposed to the heat of the paraffin 

 bath. After the material has become thoroughly heated the con- 

 tainers are examined for the purpose of detecting any leak through 

 the cork. Additional security against escape is provided by keep- 

 ing the bottles in the warm bath either upside down or on their 



