276 SEED OR MATURE OVULE. 



various colours, and becomes more or less hardened by depositions in 

 its interior. In Abrus precatorius, and Adenanthera pavonina, it is 

 of a bright red colour; in French beans, it is beautifully mottled; in 

 the Almond, it is veined ; in the Tulip and Primrose, it is rough ; in 

 the Snapdragon, it is marked with depressions; in Cotton and Ascle- 

 pias, it has hairs attached to it ; and in Mahogany and Bignonia, it is 

 expanded in the form of wing- like appendages. In Salvia, Collomia, 

 Acanthodium, and other seeds, it contains spiral cells, from which, 

 when moistened with water, the fibres uncoil in a beautiful manner, 

 having a membranous covering. In the episperm of the seed of 

 Ulmus campestris, the cells are compressed, and their sinuous bound- 

 aries are traced out by minute rectangular crystals adhering to their 

 walls. 



580. The Endopleura is also cellular. It is often thin and trans- 

 parent, but it sometimes becomes thickened. It is applied more or 

 less closely to the embryo, and sometimes follows a sinuous course, 

 forming folds on its internal surface, and separating from the episperm. 



When the embryo-sac remains distinct from the nucleus in the seeds, 

 as in Nymphaea, Zingiber, Piper, &c., it forms a covering to which 

 the name of vitellus (vitellus, yolk of an egg) was given by Gaertner. 



581. Arillus. Sometimes there is an additional covering to the 

 seed, derived from an expansion of the funiculus or placenta after 

 fertilization, to which the name arillus has been given. This is seen 

 in the Passion-flower, where the covering commences at the base, and 

 proceeds towards the apex, leaving the foramen uncovered. In the 

 Nutmeg and Spindle-tree, this additional coat is said to commence at 

 the side of the exostome, and to proceed from above downwards, con- 

 stituting, in the former case, the substance called mace ; and in the 



481 



latter, the bright scarlet covering of the seeds (figs. 481, 482). In 

 such instances, it has been called by some an arillode. This arillode, 

 after growing downwards, may be reflected upwards, so as to cover 

 the foramen. 



Fig. 481. 1, 2, 3, and 4, Various states of the arillus of Euonymus, the Spindle-tree. The 

 figures show the mode in which it is developed from the edges of the foramen, a a a a, Arillode. 

 ffffi Foramen or exostome. 



