918 



GLEANINGS IN BEE CULTURE 



THE REASONS FOR THE COLORS OF THE FLOWER 



BY JOHN H. LOVELL 



If you dip a red flower, as a rose, in a 

 weak alkaline solution, as a cup of water 

 to which a little ammonia has been added, it 

 will turn blue ; but if you dip it again in a 

 weak acid it will at once recover its original 

 red hue. A blue flower dipped in a weak 

 acid becomes red, but becomes blue again 

 in weak ammonia. In a recent number of 

 the Literary Digest there was published an 

 extract describing the color changes of red 

 and blue flowers, and their relation to an 

 acid or alkaline plant sap. 



Red and blue flowers owe their colors 

 to a large gToui? of pigments dissolved in 

 the cell-sap, and called collectively anthocy- 

 an. Yellow and gTeen pigments are usual- 

 ly in solid granules. The red and blue pig- 

 ments are believed by chemists to be derived 

 from yellcw pigments. If the sap of leaves 

 or flowers is acid, then any anthocyan pres- 

 ent is red-colored. There ai'e families and 

 genera which have the sap so strongly acid 

 that, no matter under what conditions they 

 grow, they never produce any blue flowers. 

 There ai'e no blue roses; and who ever saw 

 a blue pink? In the great orchis family, 

 which contains some 6000 species, there is 

 only one blue flower, Vanda coerulea, of 

 India. 



While red flowers are comparatively rare 

 (for there ai"e only about 257 in all north- 

 eastern America, red coloration is very com- 

 mon in leaves and stems, especially in 

 spring and fall. As to its use, if it has 

 any, there have been many opinions ; but 

 the most acceptable is that of Stahl who 

 thinks it aids the plant by absorbing heat. 

 The production of red pigment is increased 

 by three factors — a low temperature, a 

 bright light, and the presence of sugar in 

 the plant tissues. In the Alps the leaves 

 of plants are much oftener red than in the 

 lowlands, because the night temperature is 

 lower. In the intense light of alpine sum- 

 mits white lowland flowers sometimes be- 

 come red-flowered. But it is to the influ- 

 ence of sugar that the most interest at- 

 taches. 



A chemist by the name of Overton culti- 

 vated an aquatic plant (Hydrocharis) in 

 a solution of water and sugar, and in a few 

 days dark-red coloring appeared, especially 

 in the new leaves. Other plants grown in 

 pure water showed no red color. The cut 

 stems of lilies and other land plants in a 

 Aveak sugar solution soon developed red col- 

 or; while the leaves of other stems in clear 

 water remained green. He further found 

 that low temperature, l?ut above freezing, 



and bright light, promoted the formation of 

 red pigment. In arctic regions Wulff has 

 observed that the leaves of plants are often 

 ricli in sugar, and red-colored. Red au- 

 tumnal leaves are also said to contain more 

 sugar than when they were green. These 

 and many other experiments appear to 

 l^rove that there is a relationship between 

 anthocyan and sugar. 



Since plants which have a rich sugar con- 

 tent have the cell-sap colored with anthocy- 

 an, there is certainly no improbability that 

 Hie nectar secreted by such plants may con- 

 tain more pigment, or be darker colored, 

 than that secreted by plants with little or 

 no red or blue i>igments. That is, there 

 may be a relation between the color of the 

 Itoney and the amount of anthocyan a plant 

 contains, but it must be admitted that we 

 know very little about the matter. An acid 

 or an alkaline soil has apparently very little 

 effect on floral colors, for both red and blue 

 flowers grow on both kinds of soil. Still, 

 Kerner tells us that in the limestone Alps 

 several flowers are blue or yellow which 

 elsewhere have different colors. There are 

 also other observations, according to which 

 the colors of flowers have been changed by 

 chemicals, as iron or arsenic, in the soil. 

 But however it maj- be with the color of 

 nectar, its secretion is certainly strongly in- 

 fluenced by soil and climate, or Avhy should 

 alfalfa and many other plants yield freely 

 in one region and not at all in another? 



Let us in conclusion briefly consider the 

 effect of an alkaline .«ap on floAver colors. 

 In many flowers the cell-sap is only feebly 

 acid, or neutral, or alkaline; for instance, in 

 the forget-me-not and common borage the 

 sap is at first acid and the flowers open 

 red, but a little later change to blue as 

 the sap becomes alkaline. If the sap is 

 neutral the pigment may be violet-colored, 

 or it may be invisible, which explains why 

 some flowers suddenly lose their color; but 

 in this latter case it may be again restored 

 by the tise of an acid. If the sap is alka- 

 line the anthocyan ttirns blue; or if there is 

 a yellow pigment present it becomes gxeen. 

 Sometimes one part of a flower may have 

 acid and another part alkaline sap. A hy- 

 acinth has produced a flower-cluster with 

 blue flowers on one side and red flowers on 

 the other; also flowers with petals partly 

 blue and partly red. A variety of phlox 

 was clear blue in the morning, but gi'adu- 

 ally changed during the day to a beaittiful 

 deep rose. Red and blue cells may occur 

 indiscriminately in the same petal, as in the 



