54 STRUCTURAL AND PHYSIOLOGICAL BOTANY. 



439. Sometimes the central placenta extends beyond the 

 base of the carpels, rising up between them, and either form- 

 ing an adhesion with the styles, as in Geranium, or a central 

 distinct axis, as in Euphorbia. 



440. This elongation of the placenta is more apparent in 

 the fruit than in the pistil. It is analogous to the cellular 

 apex of the spadix (304) of Arum. 



441. The styles of different carpels frequently grow to- 

 gether into a solid cylinder'; Ex. Lilium. There are various 

 degrees of union between the styles. 



442. The style is incorrectly said to be divided in different 

 ways, in consequence of this adhesion. 



443. If the ovary adheres to the sides of the calyx it is 

 called inferior, and the calyx is said to be superior ; Ex. 

 Apple. 



444. If it contracts no adhesion with the sides of the calyx 

 it is called superior, and the calyx inferior. 



XIV. OVULE. 



445. The OVULE is a body borne by the placenta (412), 

 and destined to become a seed (531). 



446. It is to the carpel (406) what the marginal buds are 

 to leaves (185), and to the central placenta what buds are to 

 branches. 



447. It does not, however, appear to bear any other 

 analogy to a bud than what is indicated by its position. 



448. The ovule is usually enclosed within an ovary (396) ; 

 but in Coniferse and Cycadaceae it is destitute of any covering, 

 and is exposed, naked, to the influence of the pollen. 



449. It is either sessile, or attached by a little stalk called 

 the funiculus, or podosperm. The point of union of the funi- 

 culus and ovule is the base of the latter, and the opposite ex- 

 tremity is its apex. 



450. It consists of two sacs, one enclosed within the other, 

 and of a nucleus within the sacs. 



451. These sacs are called the primine and secundine. 



452. The primine, secundine, and nucleus, are all connected 

 with each other by a perfect continuity of tissue, at some 

 point of their surface. 



453. When the parts of the ovule undergo no alteration of 



