224 ESSENTIAL ORGANS. THE OYULE. 



the spores. Sometimes these are single, at other times united in sets 

 of two (fig. 413, 2), or of four (fig. 411, 2), or of some multiple 

 of four. There are various modifications of sporangia in other 

 Cryptogamic tribes. Thus, in Ferns, they are often surrounded by 

 an annular ring, or by elastic bands, which cause their dehiscence ; 

 while in the Chara they are called nucules, and present an oval form 

 with a spiral arrangement of tubes. 



460. The Ovule. The ovule is the body attached to the placenta, 

 and destined to become the seed. It bears the same relation to the 

 carpel that marginal buds do to leaves, and when produced on a free 

 central placenta, it may be considered as a bud developed on a branch 

 formed by the elongated axis. The single ovule contained in the 

 ovaries of Composite and Grasses, may be called a terminal bud 

 surrounded by a whorl of adhering leaves or carpels, in the axil of 

 one of which it is produced. In Delphinium elatum, Brongniart 

 noticed carpels bearing ovules, which were sometimes normal, at other 

 times mere lobes of the carpellary leaf; and in Aquilegia, Lindley saw 

 ovules transformed into true leaves, produced on either margin of the 

 carpel. Henslow has seen the ovules of Mignonette become leaves. 

 In such cases the vascular bundles of the placenta (pistillary cords) 

 are formed by the lateral veins of the carpellary leaf. These veins 

 pass into the marginal lobes or leaflets which represent ovules, and 

 seem to prove that the placenta in such cases must be truly a 

 carpellary, and not an axile, formation. Godron, from observing 

 monstrosities, says, that in Leguminosag, the pericarp or seed-vessel is 

 formed by the common petiole dilated, the style is probably the 

 terminal leaflet, or tendril, or apiculum, while the ovules represent 

 lateral leaflets of the leaf, and are modifications of it. 



461. The ovule is usually contained in an ovary, but in Coniferas 

 and Cyadacese it has no proper ovarian covering, and is called naked. 

 In these orders the ovule is produced on the edges, or in the axil of 

 altered leaves, which do not present a trace of style or stigma. The 

 carpellary leaves are sometimes so folded as to leave the ovules exposed 

 or seminude, as in Mignonette. In Leontice thalictroides (blue cohosh), 

 the ovules rupture the ovary immediately after flowering, and the 

 seeds are exposed. So also in species of Ophiopogon, Peliosanthes, 

 and Stateria. In the species of Cuphea, the placenta ultimately bursts 

 through the ovary and corolla, becoming erect, and bearing the 

 exposed ovules. 



462. The ovule is attached to the placenta either directly, when it 

 is called sessile, or by means of a prolongation called afuniculus (funis, 

 a cord), umbilical cord, or podosperm (woDj, afoot, and onl^a, a seed). 

 This cord sometimes becomes much elongated after fertilization. The 

 placenta is sometimes called the trophosperm (T^U, I nourish). The 

 part by which the ovule is attached to the placenta or cord, is its base 



