Substances Made from Foods 55 



colors are more likely to be dull, with the yellows predominant. 

 In other seasons, when cold weather is delayed, autumn coloration 

 may be brilhant and near its climax before the first frost occurs. 

 That sunlight is important in the development of the red pigment 

 in many plants may be shown also by an examination of a leaf 

 that has been closely shaded by another. The pigment stops so 

 abruptly where the shade begins that a perfect print of the upper- 

 most leaf results. An abundance of nitrogen in the soil prevents 

 anthocyan formation in some plants. This fact may explain in 

 part the greater brilUancy of colors seen on hillsides and river 

 bluffs than on adjoining floodplains. 



Among different plants there is much variation in the amount 

 of light that is required for the development of anthocyan colors. 

 This accounts for the great variation in the brilhancy of autumn 

 coloration in different years. One autumn affords light condi- 

 tions which promote the formation of anthocyan in only a few 

 trees and shrubs ; another autumn furnishes conditions so favor- 

 able that many plants become brilliant. 



Colors of fruits and flowers. The red colors of the fruits of 

 peaches, apples, and pears likewise are due to anthocyan. Here 

 again we may see the effects of sunlight on the intensity of color 

 by comparing fruits from the brightly illuminated top of the tree 

 with others from the shaded under parts. Certain varieties of 

 apples grown in the Northwestern states are more brilliant in 

 color than the same varieties grown in the Eastern states, and this 

 higher coloration is probably due to exposure to more intense 

 light. 



The red, blue, and purple colors of many flowers are due to 

 anthocyans, which are red when acid, purple when neutral, and 

 blue when alkaline. The anthocyan pigment that occurs in some 

 vegetables like beets, radishes, and purple cabbage bears no 

 relation to light. 



Other pigments. A number of other pigments occur widely 

 distributed among plants, particularly the yellow pigments of 



