180 
ORGANOGRAPHY. 
BOOK I. 
separates in the form of a third coating of the ovule 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 Papilionaceous plants, Caryophyllous 
plants, Mignionette, &c. Mirbel, who first distinguished these, 
calls them campulitropous. In both these modifications the base 
of the ovule and the base of the nucleus are the same. 
In a third class the axis of the ovule remains rectilinear ; 
but one of the sides grows rapidly, while the opposite side 
does not grow at all, so that the point of the ovule is gradually 
pushed round to the base; while the base of the nucleus is 
removed from the hilum to the opposite extremity (Plate V. 
fig. 16 — 21.); and when this process is completed the whole of 
the inside of the ovule is reversed; so that the apex of the 
nucleus, and consequently the foramen, corresponds with the 
base of the ovule. Such ovules as these Mirbel terms ana- 
tropous; they are very common: examples may be found in 
the Almond, the Apple, the Ranunculus, the cucumber, &c. 
When the base of the nucleus is thus removed from the base 
of the ovule, a communication between the two is always 
maintained by means of a vascular cord, called the raphe 
(Plate V. fig. 24. 25. /). This raphe, which originates 
in the placenta, runs up one side of the ovule, imtil it reaches 
