V. The Influence of Light upon the Growth of Leaves. 
125 
cells of the stomata and in the shealh-cells of the fibro-vascular bundles. 
A leaf taken from another part of the plant contained starch abundantly 
in its mesophyll. 
These three series of experiments together form a body of evidence 
which justifies the assertion that leaves can grow, whilst they are not per- 
forming the function of assimilation, so long as they are supplied with 
plastic material derived from other parts of the plant. 
III. Growth of leaves without Chlorophyll. 
There are three methods by means of which the forrnation of Chloro¬ 
phyll in leaves can be prevented-viz, 1) by keeping the plant in darkness, 
2) by lowering the temperalure, 3) by withdrawing from il all supplies 
of iron. 
The first of these three methods is that which is most frequenlly 
used when it is desired to obtain plants which contain no Chlorophyll. 
Planls grown in darkness, however, do not raerely differ from normal 
plants in that they possess no Chlorophyll, but as has already been poin- 
ted out, many other important modifications of structure and function 
are effected by prolonged absence of light, all of which, together with 
the absence of Chlorophyll, are expressed by the Word »etiolation«. The 
object of this series of experiments was to observe the growth of plants 
containing no Chlorophyll, but diffcring as little as possible, in other re- 
spects, from normal plants. This melhod, tlierefore, could not be used. 
The second method 1 ) may frequently be seen to be in active Opera¬ 
tion in nature. It is a common occurrence that the leaves or plants which 
require a tolerably high temperalure, such as Zea mais, Cucurbita Pepo, 
Phaseolus mulliflorus etc,, are not green in the early spring, but have 
a pale yellow colour. These leaves appear to differ from the green lea- 
\es onlv in that they contain no Chlorophyll, in size and in other respects 
they closely resemble them. This method is not a convenient one, and 
tlierefore I have not avaited myself of it. 1 have said enough, however, 
to shew that it affords evidence of the growth of leaves which are inca- 
pable of assimilating. 
The third method is that which I have adopted. I sowed seeds 
of Zea mais and ol Secale cereale in damp sawdust, and after geranna- 
lion the young plants were removed and fixed, by means of perforaled 
corks in glass vessels, in such a way, that their roots were immersed in the 
fluid which the vessels contained. The fluid had the following composilion. 
0 See Sachs: lieber den Einfluss der Temperatur auf das Ergrünen der Blätter. 
Flora 1864. 
