10 



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



groups of pigments are present in the material and to select the types o 

 preserving fluids that appear to be most nearly suitable for treating them 



Determination of Pigment Preservation Requirements 



The type of fluid required for preserving the natural color of a giver 

 specimen can often be determined with workable accuracy by estimating 

 which pigments are probably present, and then selecting the fluid thai 

 has shown itself to be most nearly suited to the requirements of these 

 pigments. With a little experience this selection can usually be made 

 without difficulty by referring to the accompanying tabulation on plant 

 pigments and to the data on preserving-fluid requirements given iij 

 table 1 . When these data prove to be inadequate for a particular speci- 

 men, its preservation requirements can usually be worked out satis- 

 factorily by applying the simple preliminary tests outlined under the 

 heading, "Preservation Requirement Tests," page 12. 



Tissue color 



Blue 



Purple 



Magenta 



Rose 



Red 



Scarlet 



Salmon 



Coral red 



Fawn 



Russet 



Brown 



Bronze 



Ivory 

 Cream 

 Light yellow 

 Pale orange 



White 



Yellow 

 Orange 

 Orange red 



Green 



Pigments probably present 



These colors and their usual variations are commonly produced by 

 anthocyanin pigmentation, except in the case of the carotenoid reds 

 and scarlets. Where complex variations involving the colors in this 

 group occur, anthoxanthins or carotenoids are commonly present as 

 copigments. Tannins and other oxidizable color-producing substances 

 also frequently occur in company with the anthocyanins. 



The more or less complex coloring represented by this group indicates 

 strong carotenoid or anthoxanthin copigmentation in conjunction with 

 anthocyanins. Tannins also often play a part in these mixed colors. 



Where pale colors of this type prevail, the anthoxanthins, which are 

 mainly flavones and flavonols, are in most instances the principal 

 pigments present. Tannins and other oxidizable color-producing 

 substances frequently occur with these pigments. 



Nearly all white flowers contain tannins or other substances that are 

 colorless in the natural state but tend to become brown or otherwise dark 

 colored when oxidized. In the case of flowers that are not pure white, 

 anthoxanthins or small amounts of carotenoid or anthocyanin pigments 

 may be present. 



The stronger yellows and oranges almost invariably indicate the pres- 

 ence of carotenoid pigments, as do also the tomato red and similar 

 orange-red shades. Mixed patterns and special shadings in this color 

 group are commonly due to anthocyanin or anthoxanthin copigmenta- 

 tion. Tannins and other oxidizable color-producing substances are 

 frequently present with these pigments. 



All green and greenish shades in plant tissue are produced by chlorophyll 

 accompanied by carotenoids. Where purple or red shades of green 

 occur, anthocyanins are also present. Tannins and other oxidizable 

 color-producing substances are also usually present in green tissue, 

 but appear to be absent in certain types. 



_ 



