195. A STEM is that part of a word which contains its meaning, and is
either a root alone or more commonly a root with an addition called a
_Formative Suffix_.
Thus, in the word #ducis#, _leader’s_, the stem, which is identical with
the root #duc-#, means _leader_; a root thus serving as a stem is called
a _Root Stem_; in #ductōris#, _leader’s_, the stem is formed by the
formative suffix #-tōr-#, denoting the agent, attached to the √#duc-#.
196. New stems are formed by adding a suffix to a stem. Thus, from
#ōrātōr-#, _speaker_, is formed by the addition of the suffix #-io-#, a
new stem #ōrātōr-io-#, N. #ōrātōrius#, _speaker’s_.
197. The noun has usually only one form of the stem. The verb has
different stems to indicate mood and tense; these stems are all based on
two principal tense stems, the present and the perfect active.