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VARIEGATION IN LEAVES.—PLASTIDS. 809 
benzol with a blue-green colour (see fig. 1148). Chlorofwein is 
another colouring matter, which, like the two preceding, is 
fluorescent, and has a yellow-green colour. These three are 
soluble in alcohol, but not at all in water, and not always in 
bisulphide of carbon. Sorby also describes other colouring 
matters which are soluble in bisulphide of carbon, and give 
different results to the foregoing with the spectroscope. 
The autumnal tints of leaves, which are generally some 
shades of yellow, brown, or red, are commonly regarded as due 
to varying degrees of oxidation of the chlorophyll which their 
cells contain, to which change Henfrey applied the term ‘ decay 
of chlorophyll.’ The experiments of M. Frémy show that the 
yellow leaves of autumn contain no phyllocyanin, and hence 
that their colour is entirely due to the phylloxanthin, either in 
its original condition or in an altered state. Strong light may 
produce a fading of leaves and other green parts, which change 
appears to be due to an alteration in the position of the grains 
of chlorophyll in the cells, and is termed epistrophe or apostrophe 
as the case may be. 
When leaves are of some other colour than green, the dif- 
ferent colours are produced either by an alteration of the chloro- 
phyll or of one of the principles of which it is formed, or in 
consequence of the presence of some other colouring agent. 
Variegation in leaves must be regarded as a diseased condi- 
tion of the cells of which they are composed ; it is commonly 
produced by hybridisation, grafting, differences of climate, soil, 
and other influences. The variegated tints are due either to 
the presence of air in some of the cells, or more commonly to an 
alteration of the chlorophyll of certain cells, or one of the 
substances of which chloropbyll is composed. (See also Colowr 
of Flowers, page 828.) To all these solid bodies contained in 
the cells and connected with its coloration or starch production, 
Schimper applies the general term of plastids. Schimper uses 
prefixes to the different plastids thus :—Starch-forming cor- 
puscles and colourless plastids which do not form starch he 
terms leukoplastids ; chlorophyll granules chloroplastids, and other 
colouring granules chromoplastids. From the observations of 
Schimper it seems that all these plastids have a common origin : 
viz. that they are the result of the division of leukoplastids, 
and never originate, as was formerly believed, by free cell-for- 
mation. Some plastids have an active life, assimilating, forming 
starch or pigments, increasing by division, &c. ; others having 
temporarily or permanently little or no vital functions, as is the 
case with many leukoplastids. Further, these passive plastids 
are frequently crystalline in form ; the active plastids, especially 
in the higher plants, being usually round. The passive crys- 
talline forms are doubly refractive. The crystaliine forms 
may become spherical, and conversely, those which are spherical 
and active may become crystalline. From leukoplastids may 
