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ON VARIEGATION IN PLANTS. 
Fig. 1.— Cornus mascula, section of a variegated leaf:— a, superior epidermis; S, inferior 
epidermis ; c, d, hairs ; e, layer of emphysematous diachyma, the seat of the variegation ; /, the 
rest of the green diachyma. 
Cornus mascula offers nothing particular either in its superior or inferior dermoidal system. Its 
malpighiaceous hairs pre- 
sent the same aspect both 
on the variegated and the 
green parts. It is not so 
■with the diachyma ; this 
presents an important mo- 
dification in its upper me- 
sophyllar system which 
has its intercellular pas- 
f l/^^-w""' sages quite full of gas or 
air, while at the same 
time the granules of chlo- 
rophyll become blanched. 
We do not say that the 
air or gas is contained in 
lacunae or air-cells, for this part of the diachyma has no proper air-cells (Fig. 1, e). The small pris- 
matic cellules are a little contracted or drawn in, in order to admit of the air lodging in the intercel- 
lular passages, which thus exist inflated by an aeriform fluid, to the 
number of six around each cellule (Fig. 2). When the decoloration 
is complete, the same phenomenon takes place in the inferior meso- 
phyllar system (Fig. 1,/.), which is naturally pierced with air-cells 
answering to the pneumatic compartments of the stomatic apparatus. 
Ordinarily, one portion of the superior mesophyllar system is affected 
with this secretion of air, while the inferior is still healthy. 
The Euonymus japonicus is still more fitted to prove that varie- 
gation has its cause in the presence of air in the passages of the 
diachyma. Fig. 3 represents a dissection of a healthy part ; and 
Fig. 4 that of a diseased or variegated part. The superior and in- 
ferior dermoidal system, the inferior mesophyllar system with its 
cellules, and air cavities remain the same, with this difference only, that the globules of chlorophyll 
are green in the one case (Fig. 3), and discoloured in the other (Fig. 4). The superior mesophyllar 
system is alone changed. On one 
side, in the healthy part (Fig. 3), 
the cellular prisms (prismen- 
chyma) firmly adhere to one 
another by the enchyma, or the 
intercellular substance which ag- 
glutinates all their partitions to- 
gether. The result is, that here 
there are no intercellular passages, 
and consequently there cannot be 
any air between the cellules. On 
the other side (Fig. 4) the cellular 
prisms of the superior mesophyll 
are detached from one another, 
having air between them at their 
six angles (Fig. 5), so that the 
passages are free from that intercellular substance which elsewhere binds the cellules to one another. 
With this development of air, or gas, or aeriform fluid, the nature of which is un- 
known, is a corresponding whiteness of the interior chlorophyll. But we regard 
this phenomenon as of less importance than the secretion of the air between the 
cellules. 
We are placed in possession of another fact not less important in the phy- 
Fig. 5.— Euonymus ja- siology of variegated leaves, by the anatomy of Syringa vulgaris (Fig. 6). In 
ponicus, variegated; the this plant, as with many others, there are several hues which constitute that 
form of variegation which we have called marbled. Some of these tints are pale 
green ; others greenish yellow, here pure yellow aboimds, and there we have pale 
Fig. 2.— Cornus mascula, variegated; 
cellules of the variegated layers, seen from 
above ; a, cellule ; b, enclosed air in the 
intercellular passages. 
Fig. 3. — Euonymus japonicus ; section 
of a healthy leaf. 
Fig. 4. 
of a diseased, or 
Euonymus japonicus ; section 
•ariegated leaf. 
&'■ 
cellular tissue of the su 
perior mesophyll, seen 
from ahove. 
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