kas^s. 
ON VARIEGATION IN PLANTS. 
I 
-£^5s§ 
213 
IP 
Fig. 6. — Syringa vulgaris ; section of a variegated leaf of different tints ; A, superior 
epidermis ; B, inferior epidermis ; a, cells of the first or upper emphysematous layer ; b, 
cells of the second do. ; c, cells of the third do. ; </, cellules of the inferior mesophyll. 
or clear yellow; at last there is a pure white, and a brown colour, which indicates a carbonisation of 
tissue. Now whence arise these varied tints, proceeding from the green to the white, by numerous 
intermediate shades ? 
We have dissected such a ^^^^Z^^^z^^z^^-z^^ - - — -^ 
portion (Fig. 6), and the ana- A JLJLlJUULjOr Jf" InHf 
tomy will soon explain this i ^~"n n— -n-^^^-^—-^-^- 
phenomenon. The discolora- 
tion of the chlorophyll, and the 
formation (secretion) of the air 
between the cellules, the em- 
physema,* — since we must here 
call the malady by its own 
name — only affects the cellular 
tissue of the superior meso- 
phyll layer by laj'er. It fol- 
lows that the first layer dis- 
eased is the superior ; the 
second, that which comes be- 
low it ; the third, that further 
down, and so on. We may, 
therefore, perceive why the 
pale-green tint is only the index of a slight superficial commencing emphysema ; why the greenish 
yellow tint indicates emphysema of several layers ; in short, why the total discoloration is also only 
the result of a general emphysema, which has spread throughout the whole diachyma. 
According to these views we must conclude that the double cause, which in one part discolours the 
chlorophyll, and in another encloses air in the intercellular passages which nominally are not destined 
to retain it, acts from above, downwards ; that is to say, it commences in the mesophyllar system, 
which is destined for the rejection of substances, and may be regarded as exercising the function of 
secretion. We have examples in the gum, resin, &c, which varnish the upper surface of leaves. 
Moreover, it is this surface which receives most light, and least humidity when the rain docs not fall 
directly on it. These observations naturally lead the mind to seek, in the effect of respiration, the 
cause of the phenomenon of variegation, which, on a close examination, is fouud to be only an 
emphysema of the cellular tissue. 
M. Sageret, who made several very interesting experiments on variegation,! attributes this pheno- 
menon to several causes, though he has not sought to resolve the question by an anatomical examination 
of the variegated parts — an essential point in a case of pathology, in which it is of the first importance 
to know the seat of the disease. According to this botanist, these causes would appear to be as 
follows : — 
1. "The seed being too old, imperfectly ripe, defective conformation, &c" — Here it is not clearly 
stated how these conditions should produce variegation ; the affirmation is vague, because it explains 
nothing. 
2. " Variegation in the parent plants." — This fact is true ; we have seen proofs of it in several 
gardens. 
3. " Accident, or injury from insects." — Here we must remark that the difference of colour in a 
leaf pierced by an insect, or which is used as its nest, is not a true variegation. This phenomenon is 
local, and caused by a degeneracy or death of the tissues, as in the growth of epiphytal cryptogams on 
the green parts of the plants. Most frequently, the yellow tint which we observe on pear and apple 
trees, &c, is only an indication of the death of the tissue. 
4. "Hybridation with a plant not variegated by the pollen of one variegated." — Hero «c must 
understand illegitimate crossing (impregnation taking place between two varieties of the same species), 
and not true hybridation (impregnation between two different species). 
5. " Imperfect impregnation, in consequence of immaturity of the pollen ;" — perhaps, more properly 
speaking, by the difference of coloration in the pollen, as has been observed in the production of the 
striatum of the corolla. 
G. "Contagion inoculated by the graft." — This result is placed beyond all doubt by daily 
experience. 
• A collection of air in the cellular tissues. 
1 Star /■' Uoym it fain naitre lei vigitmx ifeuillm panachfm. llort. Belg., 1836, p. I US, 
i 
