LESSON 21.] 



ITS COATS OR COVERINGS. 



135 



the kernel closely ; sometimes it is expanded into a wing, as in the 

 Trumpet-Creeper (Fig. 316), and occasionally this wing is cut up 

 into shreds or tufts, as in the Catalpa ; or instead of a 

 wing it may bear a coma, t r tuft of long and soft hairs, 

 such as we find in the Milkweed or Silk weed (Fig. 317). 

 The object of wings or downy tufts is to render the seeds 

 buoyant, so that they may be widely dispersed by the 

 winds. This is clear, not only from their evident adap- 

 tation to this purpose, but also from the interesting fact 

 that winged and tufted seeds are found only in fruits that split open 

 at maturity, never in those that remain closed. The coat of some 

 seeds is beset with long hairs or wool. Cotton, one of 

 the most important vegetable products, since it forms 

 the principal clothing of the larger part of the human 

 race, consists of the long and woolly hairs which 

 thickly cover the whole surface of the seed. Certain 

 seeds have an additional, but more or less incomplete 

 covering, outside of the real seed-coats, called an 



370. Aril, OF ArillllS, The loose and transparent bag 

 which encloses the seed of the White Water-Lily (Fig. SIT 

 318) is of this kind. So is the mace of the nutmeg ; and also the 

 scarlet pulp around the seeds of the Waxwork (Celastrus) 

 and Strawberry -bush (Euonymus), so ornamental in autumn, 

 after the pods burst. The aril is a growth from the ex- 

 tremity of the seed-stalk, or the placenta, 



371. The names of the parts of the seed and of its kinds 

 3I8 are the same as in the ovule. The scar left where the seed- 

 stalk separates is called 

 the Hilum. The orifice 

 of the ovule, now closed 

 up, and showing only a 

 small point or mark, is 

 named the Micropyk. The terms orthotropous, anatropous, &C. 



FIG. 31G. A winged seed of the Trumpet-Creeper. 



FIG. 317. Seed of Milkweed, with a coma or tuft of long silky hairs at one end. 



FIG. 318. Seed of White Water- Lily, enclosed in its aril. 



FIG. 319. Seed of a Violet (anatropous) : a, hilum ; 6, rhaphe; c, chalaza. 



FIG. 320. Seed of a Larkspur (also anatropous) ; the parts lettered as in the last. 



FIG. 321. The same, cut through lengthwise: a, the hilum; c, chalaza; d, outer seed- 

 coat ; e, inner seed-coat 5 /, the albumen ; g-, the minute embryo. 



FIG. 322. Seed of a St. Juhii's-wort, divided lengthwise; here the whole kernel Li 

 embryo. 



