80 Botanical Microtechnique 



sealed and returned to the oven for the next inter\al. When working 

 with deHcate material, the celloidin chip should not be dropped onto 

 the material but tied into a bag ot dry cheesecloth, which is then 

 suspended in the bottle so that the celloidin is just immersed in the 

 solution (Fig. 8.1 C) . 1 he periodic addition of celloidin is continued 



Fig. 8.1— v4, Specimen Ijottlc tor infiltration with celloidin under pressure, with 

 stopper fastened by wire loops: B. detail of wire loops for fastening cork; C, cheese- 

 cloth-bag method of thickening celloidin. 



until the solution is thickened to the degree described in the pre- 

 ceding method. 



METHOD 3 



This method is \cry slow but yields superior results. The material 

 is started in a large volume of 2*^ celloidin, at least foin times the 

 depth occupied by the material. Mark the initial \v\c\ of the solution. 

 Cork the bottle loosely, but wire the cork so that it cannot be pushed 

 out. Keep the bottle in a warm place, away from llanies or sparks. 

 Slow evaporation takes place, and. when the Noliniie is one-hall the 

 original, the sohnion is in aj)j)roximately 1', celloidin. Add new 

 4% celloidin tcj make up the original volinne. If the celloidin has 

 become colored, replace with new 4% sohnion. Continue the process 

 of slow evaporation until the material is in thick celloidin. An objec- 

 tionable featuie of method -5 was jiointed out by \\^alls (1936). If 

 the evaporation rate is too rapid, ii seems that the ether of the solvent 

 evaporates nioie lapidly than the meih\l alcohol, and the celloidin 

 jells before adecjiiate thickening is obtained. Ihis can be remedied 

 by adding a small c|uantily of j)ure ether and coin inning infiltration 

 until the j)ro|)er \iscosit\ is attained. 



