214 
ORGANOGRAPHY. 
BOOK I. 
when they are not visible. Usually it is nearly as long as 
the secundine, but sometimes it is remarkably shorter, as in 
Euphorbia Lathyris when very young (Plate V. fig. 22.). 
The outermost but one of the sacs (Plate V. fig. 23. 5, 
20. 5, 25. d) is called the secundine ; it immediately reposes 
upon the primine, and often contracts an adhesion with it, so 
that the two integuments become confounded. In order to 
ascertain its existence, it is, therefore, often necessary to ex- 
amine the ovule at a very early period of its growth. Myrica, 
Alnus, Corylus, Quercus, and Juglans have been named by 
Mirbel as plants in which the secundine is not perceptible 
(Plate V. fig. 24.). Its point is usually protruded beyond 
the foramen of the primine. 
The nucleus (Plate V. fig. 22. h, 18, 19, 20. a, 24. d, 25. e) 
is a pulpy conical mass, enclosed by the primine and secun- 
dine, and often covered by them ; but frequently protruded 
beyond the latter, and afterwards, at a subsequent period of 
its growth, again covered by them. Sometimes its epidermis 
is said to separate in the form of a third coating called the 
tercine. 
These three parts, the primine, the secundine, and the 
nucleus, have all an organic connection at some one point of 
their surface. That point is, in ovules whose parts do not 
undergo any alteration of direction in the course of their 
growth, at the base next the placenta ; so that the nucleus is 
like a cone, growing from the base of a cup, the base of which 
is connected with the hilum through another cup like itself 
(Plate V. fig. 23.). The axis of such an ovule, which Mirbel 
calls orthotropous, is rectilinear, as in Myrica, Cistus, Urtica, 
&c. ; and the foramen is at the end of the ovule most remote 
from the hilum. 
But sometimes, while the base of the nucleus and that of 
the outer sacs continue contiguous to the hilum, the axis of 
the ovule, instead of remaining rectilinear, is curved down 
upon itself (Plate V. fig. 26, 27.) ; so that the foramen, in- 
stead of being at the extremity of the ovule most remote from 
the hilum, is brought almost into contact with it. Examples 
of this are found in caryophylleous plants, Mignionette, &c. 
Mirbel, who first distinguished these ovules, calls them campy- 
