BOTANICAL TECHNIQUE 627 



ing. This shortens the imbedding time and gives smooth sections 

 in a continuous ribbon witii a relatively dull knife. 



Rau (J. Indian Bot. Soc, viii, 1929, p. 131) describes the use of 

 vacuum flasks in paraffin imbedding. See Campbell, Bot. Gaz., 

 xiii. 1888, p. 158 (chloroform method). 



For the ceresin wax method see § 177. Read also §§ 172 and 173. 



1245. Collodion Method. Introduced into botanical technique 

 by BussE {Zeit. wiss. Mik., viii, 1891, p. 462). Schering's 

 celloidin or phytoxylin, for extreme transparency, are commonly 

 used. Photographic guncotton (Jeffrey, Anatomy of Woody 

 Plants, 1926, p. 4.49) is satisfactory if transparency is not a 

 desideratum. 



The periods of immersion in the celloidin solutions should be 

 lengthened for plant material. Small delicate objects (root- 

 tips, thin textured leaves and stems) require three or four days to 

 one week ; large objects, especially blocks of wood and tissues 

 witli thick cellulose walls may require up to one month. 



The methods principally in use are approximately those of 

 Eycleshymer. It is usually best to saturate the material with 

 ether alcohol from absolute alcohol and then transfer to 2 per 

 cent, collodion solution in ether alcohol. Stopper the bottle 

 loosely to allow it to concentrate gradually. Harden in chloro- 

 form. 



Modifications have been described by Plowman {Bot. Gaz., 

 xxxvii, 1904, p. 451) for use with hard tissues. Use ten grades of 

 collodion, viz.. 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 per cent., trans- 

 ferring from one to the next. Nearly fill the bottle, clamp or wire 

 on the stopper, and put the bottle in a paraffin oven at 50-60° C. 

 for twelve to eighteen hours. After reaching 20 per cent, concen- 

 tration, add further chips of dry collodion. Blocks are cleared 

 (and left indefinitely) in a mixture of equal parts of glycerin and 

 95 per cent, alcohol. See also Bailey, Bot. Gaz., xlix, 1910, 

 p. 57, and Jeffrey, Bot. Gaz., Ixxxvi, 1928, p. 456. 



Stockwell's rapid method (Science, Ixxv, 1932, p. 291). 

 Imbed leaf and soft stem material (of Hedera and Olea) in an 

 acetone solution of collodion under reduced pressure ; the prepara- 

 tion of sections, mounted in balsam on slides, requires only fifty 

 minutes. 



See also Wetmore (Stain Tech., vii, 1932, p. 37) for the uses of 

 collodion in botanical technique. Also Carothers, Science, 

 Ixvii. 1928, p. 400 (serial sections) 



1246. Double Infiltration with Collodion and Paraffin (see 

 also § 190.) After hartleniiig in chloroform, infiltrate with 

 paraffin. This makes possible the cutting of ribbons of thinner 

 sections. 



Reichardt and Wetzel (Zeit. rviss. Mik.. xlv, 1928, p, 476) 

 use a modification of Peterfi's method for imbedding hard or 



