Q^^ BOTANICAL TECHNIQUE 



animal material owing to the impedance of the cellulose walls. 

 P'or this reason the addition of fragments of wax in the cold, 

 followed by further addition when the phial (still stoppered) is 

 on the oven top, is beneficial. Continue the additions until the 

 solvent is saturated with wax. Then place in an open dish inside 

 the oven to evaporate off the solvent. The times should be 

 shortened as much as possible consistent with the avoidance of 

 shrinkage and the distortion of the material. 



Another method is to employ a series of graded xylol-paraffin 

 mixtures, keeping the material two to six hours in each. Those 

 below the point of saturation are used at room temperature, those 

 above saturation need to be placed on or in the oven. 



According to Land {Bot. Gaz., lix, 1915, p. 397) the usual 

 procedure results in almost immediate surrounding of the object 

 by a dense layer of dissolved paraffin, since both are heavier 

 than xylol. This is not the case with the denser chloroform. 

 He recommends filling a wire gauze support with paraffin frag- 

 ments and suspending it 2 to 3 cm. above the object. Xylol 

 sufficient to rise 1 to 2 mm. above the wax is added. The stoppered 

 bottle is left undisturbed until saturation is reached. Thereafter 

 treat as usual. In the case of very delicate structures, however, 

 it is preferable to pour off the xylol-paraffin mixture repeatedly 

 down to the support, refilling the latter each time with paraffin. 

 See also Goodspeed {Bot. Gaz., Ixvi, 1918, p. 381) for another 

 procedure, and Weatherwax {Bot. Gaz., Ixviii, 1919, p. 305), 

 who considers such procedures unnecessary. 



Taylor recommends the following method : Half fill a fairly 

 deep dish (1 cm. or more) with wax and allow it to set. Place the 

 material, covered w^ith xylol, on the wax and leave until the mass 

 is of a soft pasty consistency, and then place in the oven. 

 After half to one hour replace with melted paraffin wax ; 

 make two further changes at intervals of half an hour and then 

 imbed. 



Dowson's Quick Paraffin Method {Ann. Bat., xxxvi, 1922, 

 p. 577). Material after dehydration, by concentration in glycerin 

 and its replacement with absolute alcohol, is transferred to a 

 mixture of melted paraffin (52° C. m.p.), xylol and absolute alcohol 

 in the proportion 1:2:3, and placed, stoppered, inside the oven. 

 After twenty-four hours, allow the xylol and alcohol to evaporate 

 off and imbed in fresh wax. The method is suitable for anatomi- 

 cal purposes. 



Some material, especially that containing much starch, is often 

 hard to cut in paraffin. Storage of the paraffin blocks in water for 

 several weeks softens the material and facilitates sectioning. See also 

 Couch, Science, Ixxii, 1930, p. 607. 



Veii {Ber. Deutsch. hot. Ges., 1, 1932, p. 42) uses soft wax (m.p. 

 46° C.) instead of hard and cools the block to — 3° C. prior to section- 



