558 DR. A. J. EWART ON ASSIMILATORY INHIBITION. 
the latter is more or less greenish. The green colour of the 
chlorophyll grains in such parts is not quite of the healthy 
normal shade. 
The cotyledons of Helianthus have no power of turning green 
in darkness, nor is the apparent formation of chlorophyll due to 
a photo-inductive action of the previous exposure to light when 
in the dried condition. If a very large number of seeds are 
examined, a few especially of the larger ones are slightly darker 
and more greyish, instead of almost pure white as is normally 
the case. Sections of these examined in glycerine show a 
distinct though faint yellowish or greenish tinge to be present in 
the outer epidermal layers, and in some cases in a few or many 
cells of the mesophyll tissue immediately beneath. A slight 
amount of chlorophyll may therefore be formed in the outer 
layers of the colyledons of seeds of Helianthus, resembling the 
more complete formation which commonly takes place in the 
cotyledons of maple-seeds or orange-pips ; but the chlorophyll in 
such green parts after developing in darkness for some time 
is neither as regards coloration or assimilation normal. In 
Cucurbita, in which the seeds are more completely shielded from 
light when developing, the cotyledons grown in darkness are 
always quite yellow. 
Naturally for experimentation, and for the extraction and 
testing of the pigment, only pure yellow cotyledons of Helianthus 
are employed, and in addition the etiolated leaves or cotyledons of 
Cucurbita Pepo, Lupinus albus, Zea Mays, and Phaseolus vulgaris. 
The leaves which have been grown in perfect darkness are 
dropped into water at 100° C or killed by ether or crushed in a 
mortar, brought into weak light, and after complete triturition 
extracted until a quite colourless residue is left. In Helianthus 
the cotyledons killed by hot water or ether are apt to become 
somewhat discoloured, in which case the extraction is continued 
until no more pigment can be dissolved *. Complete extraction 
with warm alcohol yields a perfectly yellow fluid, in which, by 
treatment with benzine, not the faintest trace of chlorophyll can 
bedetected. If a large amount of water is added to the alcoholic 
solution, the benzine takes up all the etiolin and becomes a pure 
deep yellow. Treatment of the etiolated material with very 
* The extraction is carried on in weak light or in darkness and in stoppered 
bottles. 
