12 



MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



5. Chlorophyll requires reducing type preserving fluids for best re- 

 sults, but can be preserved more or less satisfactorily with nonreducing 

 fluids in many instances where the presence of anthocyanin pigments 

 requires their use. The optimum pH range for chlorophyll is between 

 7.0 and 8.0. but acceptable results are often obtainable with fluids 

 having measured pH values as low as 5.5, in cases where their use is bi 

 required because of the presence of anthocyanin pigments or tannins, w 



Figure 1. — Preliminary tests with representative color-preserving fluids ma}' be re- 

 quired to determine the stabilization treatment needed for each type of plant 

 material. Wooden or plastic forceps are used to handle the samples. 



Either sorbitol borate or sorbitol citrate preserving fluids are suitable for 

 chlorophyll, but the former are generally more satisfactory where the 

 absence of flavone and flavonol pigments permits their use. 



Preservation Requirement Tests 



If the preservation requirements of a specimen cannot be suitably 

 determined through use of the tabulation on p. 10 and table 1 , the selec- 

 i ion of the proper preserving fluid can usually be worked out by applying 

 the tests (fig. 1) outlined below. 



Testing jars equipped with hold-downs and covers as described on 

 page 6 arc convenient for these tests. Grouping the jars in the order of 



