82 Bofanical Microtechnique 



When the surface of the celloidin is hard (2 niin.) , press the twig 

 gently until it is flat on the mounting block, thus affording firmer 

 support for sectioning. A batch of embedded material usually con- 

 tains more pieces than are needed for immediate sectioning, therefore, 

 only a few pieces need to be mounted on blocks. Most of the pieces 

 are merely removed from the thick celloidin, hardened in chloroform, 

 and stored in glycerin-alcohol. The pieces can be blocked at any 

 future time bv the method to be described later. 



Fk.. 8.2— Methods of mounliiig tissues on blocks for sectioning in celloidin: A, 

 cutaway view of drilled block for holding long object; B and C, cutaway views of 

 drilled bk)ck containing twig or other long object enveloped in hardened celloidin; 

 D-F, infdlrated blocks of wood and bark embedded in hardened celloiciin. oriented 

 on mounting blocks to cut transverse, radial, and tangential sedions. respectively. 



Sectors from large limbs usually must be fastened on mounting 

 blocks for sectioning. II I he j)ieces ha\e cambium and other tissues 

 of the bark, these tissues may peel off when the piece is compressed 

 in the microtome clamp. Mount three pieces from each subject, on 

 separate i)lock.s, so that transverse, radial, and tangential sections can 

 be cut (Fig. ^.2 D-f) . A generous wrapping of celloidin should en- 

 velop part of the mounting block as in Fig. 8.2. The rigidity of the 

 moiuuing of such material can be improved by mounting the material 

 in a recess that has been drilled about l/Ki in. deep into the end 

 of the mounting block. 



Blocking of pic'\ ioiisly hardened tinbttlded material is a simple 

 operation. Remove the desired pieces fiom the glycerin-alcohol 

 storage (liiid and soak in anhydrous ethyl alcohol, (-hange the alcohol 

 t\\i(c a! 1- to S-hr. iutcix ;ils. This rciiKncs the small ainoiuit of water 



