144 METHODS IN PLANT HISTOLOGY 



Kraus prepared large objects very effectively by dehydrating, 

 clearing in xylol, and then transferring to cedar oil. Sections of an 

 apple, either longitudinal or transverse, about 3 or 4 mm. thick, 

 cleared in this way, are very instructive. Strawberries, gooseberries, 

 and similar objects treated in this way afford a kind of study which is 

 too often neglected. 



Dr. LaDema M. Langdon cleared 15 mm. cubes of mature wood of 

 Dioon spmulosum in this way, but used equal parts of xylol and carbon 

 disulphide for clearing. By placing a light under the dish containing 

 the object, the bundles could be traced perfectly. 



LAND'S GELATIN METHOD 



It is sometimes desirable to get sections of partly disorganized 

 material. A matrix is necessary to hold the parts in place, but dehy- 

 dration may make the tissue unnecessarily hard to cut. 



Soak ordinary gelatin (which can be obtained at the grocery) in 

 water until no more is taken up. Then drain off the excess water and 

 liquefy the gelatin by heating. Place the material— previously soaked 

 in water— in the melted gelatin and keep it there for several hours. 

 Place also in the gelatin some small blocks of hard wood to serve as 

 supports in the microtome. The material to be sectioned is oriented 

 in a gelatin matrix on the supporting blocks, cooled until the gelatin 

 sets, and then placed in strong formalin to harden the gelatin. In 

 cutting, flood the knife with water. 



If the material is to be stained, stain it in bulk before putting it into 

 the gelatin, since the gelatin stains very deeply. Of course, the gelatin 

 could be dissolved with hot water, or hot water and acetic acid, but all 

 the advantage of a matrix would be lost. 



It would be worth while to try this method thoroughly with soft, 

 succulent tissues and with hard tissues which become still harder if 



dehydrated. 



SCHULTZE'S MACERATION METHOD 



Various solutions are used to separate a tissue into its individual 

 cells. These solutions dissolve or weaken the middle lamella so that 

 the cells are easily shaken or teased apart. Schultze used strong 

 nitric acid and potassium chlorate. Put the material, which should be 

 in very small pieces, into a test-tube; pour on just enough nitric acid 

 to cover it, and then add a few crystals of potassium chlorate. Heat 

 gently until bubbles are evolved, and let the reagent act until the 



