EOCy Bone Pt. 
DEVIATIONS FROM THE ORDINARY NUMBER OF ORGANS. 
To a certain extent the number of the organs of a 
plant is of even greater consequence for purposes of 
classification than either their form or their arrange- 
ment; for instance, the number of cotyledons in the 
embryo is made the chief basis of separation between 
the two great groups of flowering plants, the mono- 
cotyledons and the dicotyledons. In the one group, 
moreover, the parts of the flower are arranged in 
groups or whorls of five; in the other the arrangement 
is ternary. In mosses the teeth of the peristome are 
arranged in fours, or in some multiple of that number. 
So far as the larger groups are concerned, and also in 
cases where the actual number of parts is small, the 
numerical relations above described are very constant ; 
on the other hand, m the minor subdivisions, and 
especially where the absolute number of parts is large, 
considerable variation may occur, so that descriptive 
botanists frequently make use of the term indefinite, 
and apply it to cases where the number of parts is 
large and variable, or, at any rate, not easy to be 
estimated. 
Considered teratologically, the changes, as regards 
the number of organs, are readily grouped into those 
