158 COMPOUND ORGANS OF PLANTS. 



Fig. 60. 



line passes through their axis. In this instance the ovule is 

 said to be orthrotropous, (opSof, straight, and I'pdrtos, mode.) 



This is the primitive and most simple form of all ovules, 

 although not the most common. The ovules of the Urticacese 

 or nettle tribe, of the Cistace» or rock-rose family, and of the 

 Polygonaceae or buckwheat family, are of this character. 



When, however, there is an inequality in the development of 

 the parts of the ovule, either one or the other of the following 

 modes of growth will generally be the result. 



Either the hilum and chalaza will remain together and the 

 ovule will curve upon itself, so that the micropyle will be 

 brought near to the hilum, and we shall have a campulitropous 

 ovule, {xafi}<v%6s curved,) as in all cruciferous plants, (Fig. 61 ;) 

 or else the chalaza will elongate from the hilum and become 

 transported to the apex of the ovule, whilst that apex by an 

 inverse movement directs itself to the place which the chalaza 

 has abandoned. In this case, the ovule is said to be inverted 

 or anatropous, [avaipirta I subvert.) 



The curvature of the ovule in the first instance, is to be 

 attributed to an inequality in the development of its sides. 

 Thus, one of the sides of the primine possesses more energy of 

 development than the opposite side ; the former therefore elon- 

 gates whilst the latter remains stationary j and the resistance 



