PREPARATION OF SPECIMENS 13 



that the block is firmly clamped and tighten occa- 

 sionally. 



Ribbon Sections. — At times it is desirable to cut 

 a series of sections showing the variations in structure 

 in different parts of a plant organ. This is accom- 

 plished by cutting in such a manner that each section 



Eig. 7. — Ribbon Carrier. 



(Spencer.) 



with its adherent paraffin forms part of a continuous 

 strip or ribbon in which each section follows the pre- 

 ceding in regular sequence. This operation is only 

 possible with small objects, as one cannot conveniently 

 manage or mount the long ribbons resulting from large 

 specimens. Success in ribbon sectioning depends upon 

 the texture of the paraffin, the shape of the block and 

 the temperature of the knife. Very soft paraffin 

 must be used and crystallization during embedding 

 must be prevented. The edges of the block must 



