274 SEED OR MATURE OVULE. 



assume variegation, and the effect, when once established, has con- 

 tinued even after the slip was removed. The effects of grafting are 

 well seen in the case of the Eed Laburnum, when united to the Yellow 

 species. The Red Laburnum is a hybrid between the common Yellow 

 Laburnum and Cytisus purpureus, or the Purple Laburnum. The 

 branches below the graft produce the ordinary yellow laburnum 

 flowers of large size ; those above exhibit often the small purple 

 laburnum flowers, as well as reddish flowers intermediate between the 

 two in size and colour. Occasionally, the same cluster has some 

 flowers yellow and some purplish. 



8. SEED OR FERTILIZED OVULE ARRIVED AT MATURITY. 



575. While the pistil undergoes changes consequent on the dis- 

 charge of the pollen on the stigma, and ultimately becomes the fruit, 

 the ovule also is transformed, and, when fully developed, constitutes 

 the seed. After fertilization, the foramen of the ovule contracts, the 

 embryo or young plant gradually increases in its interior, by the 

 absorption of the fluid matter contained in the sac of the amnios, 

 solid nutritive matter is deposited, and a greater or less degree of 

 hardness is acquired. The seed then is the fecundated mature ovule 

 containing the embryo, with certain nutritive and protective appen- 

 dages. When ripe, the seed contains usually a quantity of starchy 

 and ligneous matter, various azotised compounds, as caseine, vegetable 

 albumen, oily and saline matters. It sometimes acquires a stony 

 hardness, as in the case of vegetable ivory, the seed of Phytelephas 

 macrocarpa. Care must be taken not to confound it with single- 

 seeded pericarps, such as the Achaenium and Caryopsis, in which a 

 style and stigma are present; nor with bulbils or bulblets, as in 

 Lilium bulbiferum, and Pentaria bulbifera, which are germs or separ- 

 able buds developed without fecundation. 



576. Seeds are usually enclosed in a seed-vessel or pericarp, and 

 hence the great mass of flowering plants are called angiospermous 

 xyyo?, or dyyeiot/, a vessel, and ani^a, a seed). In Coniferas and 

 Cycadaceae however, the seeds have no true pericarpial covering, and 



fertilization takes place by the direct application of the 

 pollen to the seed, without the intervention of stigma or 

 style. Hence the seeds, although sometimes protected by 

 scales, are truly naked, and the plants are called gyrnnos- 

 permous (yvpvos, naked, and avin/nx, a seed). Occasion- 

 ally, by the early rupture of the pericarp, seeds originally 

 covered become exposed. This is seen in Leontice, 



Cuphea, &c. In Mignonette, the seed-vessel (fig. 479) opens early, 



so as to expose the seeds, which are called seminude. 



Fig. 479. Fruit or capsule of Reseda opening early, so that the ovules become seminude. 



