1839] 



FARMERS' REGISTER. 



269 



seemed necessary to the full lievelopement of ve- 

 getable colors; in certain extraordinary circum- 

 stances, as for instance, in an atmosphere contain- 

 ing a large portion of hydrogen, or at great depths 

 in the sea, liwht does not seem to act so important 

 a part. Humboldt found several plants in the 

 subterranean galleries of the mines of Freybem, 

 which were green, although they must have 

 grpwn from the first in total darkness. The at- 

 mosphere of those mines contained, ac'^ording to 

 his observations, a very large proportion ol' hydro- 

 gen. At another time, he Ibund near the Cana- 

 ries, a fucus which was bright grass-green, al- 

 though it had grown at a depth of 180 leet from 

 the surface of the water. The licht by which this 

 fucus was illuminated whilst growing, according 

 to the laws which are known to govern light when 

 traversing water, must have been 200 times less 

 than that of a candle at a foot distance. 



'J'he effect of solar light upon plants, is to fix 

 carbon in their tissues. Hence it is natural to con- 

 clude, that this operation is connected with the 

 production of color. In fact, when it takes place, 

 coloring ensues ; when it does not fake place, the 

 organs preserve the primitive white color of their 

 tissues ; and when it has taken effect incompletely, 

 the results are of an intermediate character. The 

 deposition of carbon thus effected, does not ope- 

 rate upon the vegetable membrane; that always 

 retains its original pearly lustre. But by effi^cting 

 a combination with hydrogen and oxvgen it forms 

 a peculiar substance, termed a chromule. the abun- 

 dance or scantiness of which determines the tint 

 of the leafy surface. The tissue, no doubt, pro- 

 duces some effect, by reason of its own pallid hue, 

 or its density, or the hairs wi'h which it is cover- 

 ed, or the air which it contains. How it is that 

 tlie union of these elements produces such a vari- 

 ety of colors; or how it is that carbon, which is 

 black, united to oxygen and hydrogen, which are 

 colorless, can give rise to any other color than 

 black, we can no more explain, than we can, how 

 it is that copper, which is reddish-brown, and ni- 

 tric acid, which is colorless, form the beautiful blue 

 ealt which they do. We only know these things 

 as facts; and until we better understand the nature 

 of chemical union, we cannot expect to know any 

 thing more about tliem. Some of the older phy- 

 siologists attempted to account for the green color 

 ■of leaves, by supposing that the color of charcoal 

 was not black, but a very intense blue ; and that 

 shining through the yellow sides of the cells, the 

 combination of the two colors produced green. 

 This notion, however, is disproved by the most su- 

 perficial examination; forthe coloring matter may 

 be separated from the tissues with the greatest Ri- 

 cility, and it still preserves its color ; and besides, 

 the yellow of the tissues, if any, is so excec!'' -'riv 

 feeble, as to be wholly unable to cause the bliic of 

 the carbon to appear green, if the carbon were in- 

 deed blue. 



Leaves which are usually green, assume differ- 

 ent colors, when about to decay. It is common to 

 see, in the autumn, this green change into yellow, 

 as in the Lombardy poplar; or red as in the su- 

 mach, and some kinds of oak. It has been ascer- 

 tained, that in such cases, shortly before the change 

 takes place, the leaves cease to exhale oxygen in 

 sun-light, but do not cease to absorb it at nisht; 

 hence it is inferred, that the chromule is oxydized, 

 ^'hich at first brings on a yellow, and afterwards 



a red color; for the most decided red, always be- 

 gins by a change to yellow. It has also been re- 

 marked, that red colors are most conmion in leaves 

 which contain some kifid of acid, as in the vine, 

 the sorrel, &c. The red coloring matter obtained 

 from such leaves forms an mfusion, which, like that 

 obtained from red flowers, becomes more intense, 

 Vi'hen acted upon by an acid. The infusion of 

 yellow leaves is affected by the action of alkalies, 

 in a manner precisely like that of yellow flowers; 

 ('. e. is changed to a reddish brown. Hence some 

 have supposed, that whilst red is owing to the de- 

 velopement of an acid, others colors may be as- 

 cribed to the presence of an alkali. 



The puncture of an insect, the attack of a para- 

 sitical fungus, or an early frost, may produce a 

 change in the color of a leaf, or part of a leaf; and 

 what is worthy of remark, the colors thus acci- 

 dentally produced, are the same which the plant 

 would have taken of itself in the autumn. Thus 

 accidents turn the leaves of the poplar and lilac 

 yellow, of the sumach and pear tree, red. This 

 would seem to indicate that the colors are pro- 

 duced m accordance with some fixed law, and by 

 a change in some element which exists at all 

 times in the plant. In many plants, the leaves 

 which grow in the vicinity of the flower, frequent- 

 ly present various tints, and these tints are almost 

 always in unison with the flowers which they ac- 

 company ; thus in the euphorbias, they are white, 

 in the amaranthus melancholiciis (love-lies-bleed- 

 ing) they are red. 



VViih respect to the relation which colors bear 

 to each other, they have been divided into two 

 series. Those of one series, have yellow for their 

 typical color, and are capable of passing into red 

 or white, but never into blue ; those of the other, 

 have blue for their typical color, and are capable 

 of passing mto red or white, but never yellow. 

 Green is considered to arise from an equilibrium of 

 the two. De Candolle calls the first series xan- 

 thic, from the Greek word meaning yellow, and 

 the other cyanic, from the Greek word meaning 

 blue. Upon this principle he has constructed the 

 follovvinff scale. 



Red, 



Orange-red, 



Orange. 



Orange-yellow, 



Yellow, 



Yellow-green, 



Green, 



Greenish-blue, 



Blue, 



Violet-blue, 



Violet, 



Violet-red, 



Red, 



1 



f- Xanthic series. 



I 

 1 



J 



Equilibrnun. 



y Cyanic series. 



1 



I 



J 



~It will be at once remarked, in considering this 

 table, that all the flowers capable of changing 

 their colors, do it, by rising or descending in the 

 series to which they belong. Thus the flowers of 

 the rose, which belong to the xanthic series, in 

 one species is yellow, in another red, and in ano- 

 ther white, but never blue. The anemone, which 

 belongs to the cyanic series, varies liorn white on 

 the one hand, to violet-red and red on the other, but 

 never yellow. Although there are certain excep- 

 tions to this rule, particularly in the hyacinths, some 

 of whose varieties approach the xanthic series, al- 



