Saccident Leaves in the Wall-Flower. 
4i 
concavity upwards), and may be as much as four times as thick as 
normal leaves. Fig. 62 shows the proportional dimensions of the 
succulent and normal leaves in transverse section. 
Fig. (! 2 . 
Transverse sections of leaves of wall-flower treated with nitrate of silver 
and blackened by exposure to light. A, resistant leaf; B, succulent 
leaf: from photographs. 
The structural features agree with Lesage's description. The 
palisade-cells, which normally form several layers and reach from 
the upper epidermis to the vascular bundles, have become very 
much elongated, the remainder of the mesophyll (between the 
bundles and the lower epidermis), which is normally lacunar and 
mostly of the nature of spongy parenchyma, may sometimes 
become largely converted into palisade-tissue, the intercellular 
spaces being then very much reduced. 1 This change appears to be 
due chiefly to increase in size of the cells, with little or no cell- 
division. The chlorophyll-grains also become reduced in size, 2 as 
w^as observed by Lesage in other plants, even in wild maritime 
forms, e.g. that of Thesium humifusum (Revue Gen. de bot., II., p. 106). 
One of the four seedling plants (the one omitted in the above 
description) appeared for a long time to be entirely unaffected by 
the treatment w r ith salt, but, by the time the experiment ended, 
some of its lower leaves had become somewhat thickened and 
brittle. Its resistant nature was probably in some way connected 
with its differing varietally from the other plants experimented on. 
It agreed with two or three of the control seedlings, but differed 
from all the other plants in having smaller, darker green leaves and 
a more compact habit. 
1 Thus here and there practically the whole thickness of the 
mesophyll may be composed" of palisade-tissue. 
2 To some extent this may be regarded as a pathological 
phenomenon, but apparently it is no more so than in the 
garden Wall-flower near the sea. The diminution of starch - 
formation in salted and maritime plants (Lesage, Comptes 
rendus, CXII., p. 672) need not be specially referred to here. 
