140 
dusky green hue through the red covering which in- 
vests it. So, likewise, those portions of leaf, which 
have been infused in water or alkohol, and thereby 
nearly deprived of colour, become red or green, ac- 
cording as they are immersed in acid or alkaline li- 
quors ; and the same may be said of the substance 
of the parenchyme, from which the epidermis has 
been previously removed. Hence the same coloura- 
ble matter resides in the leaves of the red cabbage as 
in those of the green variety, as is thus manifested by 
its undergoing the same effects, when exposed to the 
operation of the same agents. Consequently, the 
difference of colour in the two varieties is to be sought 
in that of the epidermis alone. 
394. Now, the cause of the red colour in this epi- 
dermis appears to be that same predominance of acid, 
which occasions it in other instances ; for the red 
tint, which these leaves afford to alkohol, is not af- 
fected by exposure to the air, but is exalted by acids, 
and rendered green by alkalis ; and these transmuta- 
tions of colour may be indefinitely repeated. If, far- 
ther, the epidermis be raised, and carefully removed 
by dissection, it will be changed instantly to a rich 
green colour by immersion in an alkaline liquor, and 
may be again restored to a red hue by plunging it 
in an acid ; but if the immersion in alkali be pro- 
longed, the colourable matter dissolves, and the green 
tint passes into yellow. If, also, pieces of the entire 
red leaf be immersed in acid liquors, the edges of 
the parenchyme soon change from green to red, and 
the colour of the epidermis is at the same time con- 
siderably heightened j while^ in alkaline fluids, simi- 
