180 ORGANOGRAPHY. BOOK I. 



separates in the form of a third coating of the ovule called the 

 tercine. 



T'hese 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 

 iniderffo 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. 

 ^Vhen 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. e, '25. f). This raphe, which oi'iginates 

 in the placenta, runs up one side of the ovule, until it reaches 



