The Pentacyclidce. 
J 53 
The invariable presence of a unilocular ovary distinguishes the 
Primulales sharply from the other two cohorts of Pentacyclidre; 
the ovary is unlobed; and the number of carpels is further masked 
in the Primulaceae and Myrsinaceae by the condition of the style, 
which is undivided, capitate, with a simple stigma. In the 
Plumbaginaceae, which include about 20% of the total number of 
species in the cohort, five styles are present, suggesting isomery of 
the gynaecium with the corolla. 
The number of carpels in Primulaceae and Myrsinaceae has 
been made the subject of considerable attention, but research has 
failed hitherto to ascertain it at all definitely. The number five,— 
i.e., isomery with the corolla—has appeared to be the most likely, 
and this has been hinted at by several considerations, such as the 
appearance of five or ten teeth in connection with the dehiscence 
of the capsule in many Primulaceae; the appearance of five leaves 
in the place of an ovary in certain abnormal forms of Primula, and 
other phenomena in structure and development 1 ; the presence of 
five styles in the allied Plumbaginaceae, etc. 
The detailed discussion of this question is outside our province; 
nor, indeed, is its solution of such fundamental importance for our 
purpose as at first sight may appear. In the other two cohorts of 
Pentacyclidae the ovary is multilocular, and the carpel-number is 
determinate ; but in the Primulales the flower differs so essentially, 
apart from the gynaecium, from those of Ericales and Ebenales, 
that there can be little question of close affinity between the two; 
the comparative structure of the ovary thus loses much of its 
significance. We have, in fact, to search in a direction different 
from that of the ericalian stock for the ancestry of the Primulales ; 
not only the Sympetalae as a whole, but the subordinate group of 
Pentacyclidae also, we shall find, are very probably polyphyletic in 
origin. 
In Myrsinaceae and Primulaceae the ovary is usually multi- 
ovulate, although a distinct tendency to reduction in the number of 
ovules is observable; and in Myrsinaceae all but one usually abort 
at maturity, and the fruit is one-seeded. In Plumbaginaceae the 
unilocular ovary contains invariably but one ovule, placed basally. 
The ovules in the first two natural orders are borne upon a so-called 
“ free-central ” placenta, a structure continuous with the floral axis 
and projecting into the ovary chamber. 
1 See T. G. Hill. “ On Variation in the Flowers of certain species 
of Primula .” Ann. Bot., XVI (1902), p. 317, where relative 
literature is cited. 
