OVULE. 55 



position during their growth, thfe two sacs and the nucleus are 

 all connected at the base (449) of the ovule, which is orthotro- 

 pous or atropous. 



454. And then the base of the nucleus and that of the 

 ovule are in immediate connection with each other. 



455. But the relative position of the sacs and the base of 

 the ovule are often entirely altered during the growth of the 

 latter, so that it frequently happens that the point of union of 

 the sacs and the nucleus is at the apex (449) of the ovule. 



456. And then the base of the nucleus is at the apex of the 

 ovule. 



457. In such cases, a vascular connection is maintained be- 

 tween the base of the ovule and the base of the nucleus, by 

 means of a bundle of vessels called a raphe. 



458. The normal position of this raphe is on the side of the 

 ovule, next the placenta. 



459. The expansion of the raphe, where it communicates 

 with the base of the nucleus, gives rise to the part of the seed 

 called the chalaza (548). 



460. When the ovule is curved downwards so as to ap- 

 proach the placenta, it is campylotropous ; when curved down- 

 wards and grown to the lower half, anatropous ; when at- 

 tached by its middle so that the foramen is at one end and the 

 base at the other, it is amphitropous. 



461. The mouths of the primine and secundine usually con- 

 tract into a small aperture called the foramen of the ovule, or 

 the exostome. 



462. The apex of the nucleus is always applied to this 

 foramen. 



463. In consequence of the relation the base of the nucleus 

 bears to the base of the ovule, the foramen will be at the 

 apex of the ovule when the two bases correspond, and at the 

 base of the ovule when the two bases are diametrically 

 opposite. 



464. The foramen indicates the future position of the radi- 

 cle of the embryo (555) ; the radicle being always next the 

 foramen. This is a fact of great importance in practical 

 Botany. 



465. Within the nucleus is a cavity or bag, called the sac 



