SYMPETALOUS EXOGENS 455 
Sub-Class II. SYMPETALAE 
Called also Gamopetalae, or Monopetalae 
Plants, the flowers of which nearly always have both a calyx and 
corolla and which have the petals more or less united at the base, 
forming a corolla, which seems to be a single, undivided or only 
partially divided envelope. 
SYMPETALOUS OR MONOPETALOUS EXOGENS 
Of the groups of plants thus far described we have found either 
an absence of petals or when, as in the greater number of groups 
there has been present a corolla, it has consisted of several petals, 
as in case of the rose, the buttercups, and the members of the 
pea family. 
In case of the sub-class now to follow, the general rule is that 
all the petals are so united as to appear as a single member, as in 
the morning glory and the blue bell. To this complete union there 
are, however, some exceptions, for the clethra and some of the 
pyrolas and even some plants of the heath family besides a few 
others, have corollas divided nearly or quite to the base, thus form- 
ing an envelope of several petals. Other characters of these plants 
hold them in the sub-class to which they really belong, yet to which 
they form, in respect to the petals, exceptions. Thus, for example, 
the corolla in some pyrolas is composed of a single member with 
moderate sinuses between its 5 elementary parts. In case of other 
pyrolas the sinus is so deep that the corolla is practically divided 
into 5 distinct petals. Yet these pyrolas are evidently closely allied 
to each other. 
In a few cases, as in Fraxinus and Glauz, the corolla is absent. 
In general the calyx has 5 points and, as we observe in the 
morning glory, the corolla is usually 5 pointed. 
There are, in a considerable group, 5 stamens; in another group 
this number is doubled, while in still another group there may 
be less than 5 or more than 10 stamens. 
