136 MORPHOLOGY, OE COMPARATIVE ANATOMY. 



ovules, so that no representative of the stylar or stigmatic regions 

 exists here. Among the Oonifene, Pinus and its allies have scale- 

 like carpels with a pair of ovules on the upper surface, at the base 

 (fig. 266) ; the structure is analogous, although the form of the 

 scale differs, in Thuja ; the Cypress has peltate scales, with nume- 

 rous ovules ; in Juniperus each of the three scales has only one 

 (tig. 267). In Taxus the ovule is a solitary structure, a kind of 

 free ovule, growing out from the apex of a small cone formed of 

 barren scales. In the Cycadacese, Cycas has large leaf -like car- 

 pels, with numerous marginal ovules; Zamia has peltate scales, 

 more like Cupressus, with the ovules pendent from the thickened 

 summit. 



By some authors what is above described as a naked ovule is thought 

 to be an ovary (see under Gynmosperms). 



Sect. 10. PRODUCTS OF THE ESSENTIAL ORGANS OF FLOWERS. 



Ovules. Ovules are the rudiments of seeds, and arise from the 

 placentas situated in the ovaries of Angiospermous plants (figs. 

 253-255), and on the margins or surface of the open carpels of 

 Grymnospermia (figs. 266, 267). They originate as cellular papillae 

 at an early stage of development of the ovary, and acquire a definite 

 form and structure by the time the flower expands. 



Ovules are by some observers regarded, in part at least, as a kind of 

 bud ; for not only do they appear in the positions occupied by adventi- 

 tious buds on vegetative leaves, as in BryophyUwn, but abnormal leaf-like 

 carpels often bear bulb-like structures and foliaceous lobes, in place of 

 the ovules, on their free margins. By others they are considered, at 

 least so far as their outer coat is concerned, to be modified leaves or 

 portions of such leaf. In most cases they originate from the margins 

 or surface of a carpellary leaf; but in some cases they originate from 

 the axis (free central placentation), and are then either lateral or 

 terminal, as in Piperaceae, where the end of the axis becomes the 

 nucleus of the ovule. Other illustrations are afforded by Taxus and 

 Polygonum. 



Number. The number of ovules in the ovary, or in one cell of 

 a compound ovary, varies between wide limits. Thus the ovule is 

 solitary in the simple ovaries of Ranunculus, Prunus (fig. 245), &c., 

 in the compound ovaries of Polygonaceae &c., and in each cell of 

 the bilocular ovaries of the Umbelliferse &c. ; the number is still 

 small and definite in the simple pistils of many Leguminosae, in the 

 cells of the compound ovary of Quercus, &c. ; in a very large pro- 

 portion of compound ovaries, whether unilocular or multilocular, 

 the ovules are very numerous on each placental surface, and they 

 are termed indefinite, as in Primula, Papaver, &c. &c. 



