382 
DUNCAN S. JOHNSON 
lest sort of internal structure with slightly specialized palisade cells 
and but one, or in places two other layers of mesophyll cells. All in all 
the internal structure of this Peperomia is the simplest thus far describ- 
ed within the genus. This means also that it is the simplest within the 
family. 
The question arises as to whether this simplicity is primitive or not. 
The more generally accepted views of the character of primitive angio- 
sperms, which were probably dicotyledonous, conceive them to be tree- 
like or shrub-like woody plants (Wettstein, 191 1, p. 196; Arber and Pa- 
arkin, 1907; Maneval, 1914; Engler and Gilg, 1912; p. 156). It is clear 
that all these writers must regard this Peperomia as far removed in 
vegetative structure from the most primitive type for the dicoty- 
ledons. The tree-like Pipers though not the most primitive dicots in 
stem structure seem clearly the more primitive members of the Piper- 
aceae. P. hispidula on the other hand must be regarded as among the 
most highly specialized members of this family, in most points of 
vegetative structure. 
2. Development and structure of flower and fruit. — In treating these 
topics it will not be necessary to discuss in detail the much disputed 
question of the relative primitiveness of unisexual and hermaphrodite 
flowers among angiosperms nor to decide whether naked flowers are 
sometimes primitive, as well as sometimes due to reduction. One or 
two points showing the relative simplicity of this Peperomia in its own 
family seem reasonably clear. In the first place all the flowers are 
potentially hermaphrodite and there is no variation in the number of 
microsporangia formed in each stamen, such as occurs in some other 
Piperaceae (Johnson, 1910). This number, however, is but two, a 
very unusual number among angiosperms. The same number of 
microsporangia per stamen is found throughout the genus Peperomia^ 
while in other Piperaceae, and in nearly all other angiosperms, four 
sporangia are found in each stamen. Evidently P. hispidula, along 
with the others of its genus, is decidedly aberrant or specialized in this 
respect. The development of the stamen, of the microspore, and of 
the male prothallus is like that of the vast majority of angiosperms. 
The history of development indicates very definitely that the 
carpel of P. hispidula is single, as there is not the slightest trace of its 
having a compound origin. Yet the carpels of its nearest allies the 
Pipers show rather definite evidence, in the presence of three lobes in 
the stigma and of six vascular bundles in the wall of the ovary, that 
