90 Botanical Microtechnique 



Celloidin-Paraffin Double Embedding 



Double embedding consists of infiltrating and embedding tissues in 

 celloidin and then infiltrating with paraffin. This procedure is used 

 with materials that combine hard tissues ^vith regions of very fragile 

 and brittle tissues. The stems of some grasses and sedges do not 

 become well infiltrated by celloidin, but paraffin penetrates well. The 

 material has regions of highly lignified sclerenchyma, requiring more 

 support than that afforded by paraffin alone. 



Embed in celloidin by one of the foregoing processes and harden 

 well in chloroform. Trim away the enveloping celloidin, exposing all 

 cut surfaces but leaving intact the outer surface of the epidermis. 

 Some workers use clearing oils or mixtures that clear or make the 

 tissues transparent. This does not necessarily improve the subsequent 

 infiltration and usually aggravates brittleness. It is adequate to change 

 the chloroform several times to eliminate the celloidin solvent and to 

 proceed with infiltration in paraffin. The embedded material may be 

 cut and ribboned on a rotary microtome; very firm material must be 

 cut on the sliding microtome. 



