34 Botanical Microtechnique 



infiltration and a water-jacketed oven set for 52 to 55°C. for tlie final 

 operations. 



DEVICES FOR CASTING BLOCKS 



Several methods are in use for casting the embedded tissues into 

 a mold. The most practical mold is a paper tray or boat made from 

 strong glazed paper, such as herbarium mounting paper. The method 

 of making boats is illustrated in Fig. 5.1. Fold and crease along the 

 dotted lines; the narrower fold is slighth more than the desired 

 depth of the boat, the wider fold is nearly twice as wide. Fold as 

 shown in B, lapping the wide side to lock the narrow side. Small 

 unattached objects like spores or minute seeds are cast in a pyramid 

 mold (Fig. 5.1 C). 



Soak the boats in smoking hot canning wax until bubbles cease to 

 come from the paper. Remove the boats from the wax, shake off 

 surplus wax and cool the boats on a paper towel. A supply of wax- 

 soaked boats of various sizes can be |)iepared in ad\ancc and used as 



r i 



1 1 



i i 



_ _ 1 



Fig. 5.1-Mii1i(hI of laving oul (A) and folding (B) paper boats for casting paraffin 



blocks. C, pyramid mold. 



needed. It is probable that a boat formed from a llexible plastic 

 will eventually be developed. 



Some form of hot plate is used to kcc'i) ilie parallin in tlu boat 

 melted while the material is being arranged. Electric plates with 

 thermostatic control are available. A sheet-copper table is used in 

 many laboratories. An easily controlled heating table consists of a 

 sheet of V2-in. boiler plate, (i to H in. wide and 18 to 24 in. long, 

 mounted on legs or on a large ring stand (Fig. 5.2) . 



Fhe warm-pan method must be used foi materials that arc very 

 small. l)uo\ani, or irans|)areiit. Vhv boat is sujjported on a wire 



