FLOWER BUDS OF APPLES 273 



Of the various rea-ients tried a modification of Drinkard'.s 

 (8) formula for Gil son's mixture gave the best results in kill- 

 ing and fixing the material and was used ihroug'hout. The 

 modification consisted of increasing" tlie percentage of alcohol 

 from ten to twenty-five to facilitate penetration through the 

 pubescence of the buds. The material was left in the ddlling 

 fluid from ten to twenty hours, the length of the period depend- 

 ing upon the size of the buds. 



Dehydrating or the removing of all traces of water from the 

 tissues was accomplished by means of increasing strengths ot 

 alcoholic solutions. Two hours was taken as the minimum time 

 allo-wed for the material to remain in each solution. 



In the 50 per cent, 60 per cent, and 75 per cent alcohols iodine 

 was added to remove the mercury from the ti'>sues, while the 85 

 ])er cent and 95 per cent alcohols contained 10 per cent of 

 glycerine in which the buds were left for twenty-four hours to 

 toughen the tissues and prevent brittleness, after wnich they 

 were removed to absolute alcohol. The material was removed 

 from absolute alcohol and run two hours i^n each of six solutions 

 of different percentages of xylol which cleared the tissues and 

 also prepared them for infiltration with paraffin. 



The last two sets of buds were run through 25 per cent, 59 

 per cent, 75 per cent, and 100 per cent solutions of cedar oil 

 for clearing, with the result that the material handled in this 

 way was not nearly so brittle as the material cleared in xylol 

 and could therefore be sectioned much thinner. This point was 

 observed in running up material where thin sections were desired 

 for the study of heterotypic mitosis. 



It was found best to very gradually infiltrate the flower tissue 

 with soft paraffin which was later replaced with medium and 

 then hard paraffin (56° — 58°C). The best results were obtained 

 by imbedding the material in blocks of paraffin which were com- 

 posed of four parts Leitz best grade of hard paraffin and one 

 part Parowax. This mixture gave a grade of paraffin with a 

 melting point of about 55° C. and with a toughness that the hard 

 paraffin alone did not afford. 



During the eight to ten hours that the material was in the 

 paraffin oven the temperature of the oven was not allowed to 

 rise over three degrees above the melting point of the paraffin 

 used. This was very important Ijecause if the temperature was 



