30 ELEMENTS OF PLANT ANATOMY. 
occasionally found in other plants, not connected with any 
particular structure, but this is supposed to be a pathological 
rather than normal appearance. 
The chloroplastid, then, consists of a protoplasmic frame- 
work and a green pigment. In phanerogams, vascular crypto- 
gams, and nearly all Bryophytes, this framework takes the form 
of a small spherical or egg-shaped body. In one of the groups 
of Bryophytes, Anthoceroteae, only one large plastid occurs in 
a cell. In the algae plastids occur in various forms, such as 
spiral bands, rings, stars, and other singular shapes. 
The pigment can be abstracted by the use of absolute 
alcohol, leaving the framework behind as a colorless, somewhat 
porous substance, having the same chemical nature as the 
remaining protoplasm. If benzol be added to the solution of 
the pigment in alcohol, a yellow substance is separated out 
which remains in the alcohol, the green of the chlorophyll going 
over to the benzol. This yellow substance has been named 
Xanthophyll. It is present in the chloroplastid, but whether 
in addition to the chlorophyll itself, or forming an integral part 
of the pigment, is not known. 
An alcoholic solution of this chlorophyll pigment has the 
quality of fluorescence. When seen in reflected light it appears 
opaque and of a deep red color. If the ight which has been 
passed through a layer of a moderately strong solution be 
examined with the spectroscope, characteristic absorption bands 
will be seen. Chemically considered the pigment is’ a combina- 
tion of carbon, hydrogen, oxygen, and nitrogen, with no iron in 
it, but it is never formed unless iron be present in the tissues. 
With some few exceptions its production is also dependent 
upon light. When an insufficient amount of light is present, 
a substance named etiolin is formed, which in color resembles 
Xanthophyll, but is not supposed to be identical with it. 
In the chloroplastid, in connection with the action of light, 
a carbohydrate originates, probably a formic aldehyde, which 
