more water is consolidated in the formation of 
bread from barley, and still more in that from oats ; 
but the gluten in wheat, being in much larger quan- 
tity than in other grain, seems to form a combin- 
ation with the starch and water, which renders 
wheaten bread more digestible than the other spe- 
cies of bread. 
The arrangement of many of the vegetable prin- 
ciples in the different parts of plants has been 
incidentally mentioned in this Lecture $ but a more 
particular statement is required to afford just views 
of the relation between their organization and 
chemical constitution, which is an object of great 
importance. The tubes and hexagonal cells in the 
vascular system of plants are composed of woody 
fibre ; and when they are not filled with fluid mat- 
ter they contain some of the solid materials which 
formed a constituent part of the fluids belonging 
to them. 
In the roots, trunk, and branches, the bark, 
alburnum, and heart- wood, the leaves and flowers ; 
the great basis of the solid parts is woody fibre. It 
forms by far the greatest part of the heart- wood 
and bark ; there is less in the alburnum, and still 
less in the leaves and flowers. The alburnum of 
the birch contains so much sugar and mucilage, 
that it is sometimes used in the north of Europe 
as a substitute for bread. The leaves of the cab- 
bage, broccoli, and seacale, contain much mucilage, 
a little saccharine matter, and a little albumen. 
From 1000 parts of the leaves of common cabbage 
I obtained 41 parts of mucilage, 24 of sugar, and 
8 of albuminous matter. 
