THE MOLECULAR FORCES IN PLANTS. 



191 



wheat-grain readily permits the water to penetrate into the inside 

 of it. To acquaint ourselves with the anatomical structure of the 

 fruit-coat and seed-coat of the wheat, we make the sections, which 

 must be as thin as possible, from grains which have not been in 

 water too long, and treat them before observation with potash 

 solution. Fully soaked grains are unsuitable, since it is very 

 difficult to prepare good sections from them. The potash causes 

 the tissues to swell up, so that the details of structure of the 



-f 



FIG. 71. Triticum vulgare. A, transverse section through, the coats; ep, epidermis; 

 , adjoining layers ; chl, chlorophyll layer : these all belong to the fruit-coat ; ii, derived 

 from the inner integument ; n, the outermost layer of the nucellus : these together form the 

 seed-coat; al, aleurone grain layer of the endosperm. Magn. 240. 



B, medium longitudinal section through the lower part of a ripe fruit. To the left, 

 below, the embryo, with sc, the scutellum; V, its ligule, and vs, its vascular bundle; ce, its 

 cylindrical epithelium ; c, sheathing part of the cotyledon ; pv, vegetative cone of the stem ; 

 hp, hypocotyl ; I, ligule; r, radicle ; cp, root-cap of the radicle ; cl, root-sheath ; m, point of 

 emergence of the radicle, corresponding with the micropyle of the ovule; p, the fruit- 

 stalk, and vp, its vascular bundle ; /, side wall of the fruit. Maga. 14. (After Strasburger.) 



fruit-coat and seed-coat become fairly distinct (see Fig. 71). The 

 fruit-coat consists of the cuticularised epidermis, ep, a layer of 

 parenchyma, e, and a wide layer adjoining these, whose elements 

 are tangentially elongated, chl. The seed-coat is composed of 

 several layers, but the cellular structure of the outer layers, ii, 

 cannot be properly made out, and they present themselves for the 

 most part merely as brown strips. The innermost layer, n, of 

 the seed-coat, which lies immediately below these brown strips 





