LECTURE III. 
83. When a plant begins to produce flowers, a great 
change occurs in its manner of growth, sometimes 
suddenly, sometimes extended over a considerable 
time. If the appearance of a flower is sudden, 
there is little alteration among the leaves antecedent 
to the appearance of the flower; but when the 
flowers appear slowly, several intermediate forms 
have to be noticed before the flower itself. Of this 
some indication is found in the sweet-scented Colts¬ 
foot ( Tussilago fragrans). The ordinary leaves of 
this plant are long-stalked, and almost circular, with 
a heart-shaped base. Such leaves are replaced by 
degrees by bodies of the same kind as themselves, 
but of different dimensions and a different form. For 
instance, shortly above the bottom of the stem, the stalk 
of the leaf is widened enough to surround the stem com¬ 
pletely at the base; but of that circumstance scarcely a 
trace could be found in the beginning. A succession 
of similar and gradually increasing differences will be 
seen to follow, each imperfect leaf becoming more 
and more unlike the first, till at last we reach the 
parts among which the flowers are produced. Now, 
this gradual diminution of magnitude, this change 
from one condition to another, is extremely common 
in the branches of plants producing flowers; and all 
the circumstances belonging to it require to be care- 
