. Carnegie Institution of Washington publication. STRUCTURE. cover two seeds with ease. Its cells (Fig. 41, c-e) are tubular and stretched out in the direction of its growth, thin-walled, and somewhat pointed. In they are about three times longer and wider than in N. odorata and caerulea. The inner layer of cells adheres closely to the seed, and its cells are much smaller than those of the outer layer. The walls are supplied with fine pores (Weberbauer). The aril serves, by its mucilage and inclosed air, to float the seed for a short time ; it drops the seed in the course of a few hour
. Carnegie Institution of Washington publication. STRUCTURE. cover two seeds with ease. Its cells (Fig. 41, c-e) are tubular and stretched out in the direction of its growth, thin-walled, and somewhat pointed. In they are about three times longer and wider than in N. odorata and caerulea. The inner layer of cells adheres closely to the seed, and its cells are much smaller than those of the outer layer. The walls are supplied with fine pores (Weberbauer). The aril serves, by its mucilage and inclosed air, to float the seed for a short time ; it drops the seed in the course of a few hours (N. tuberosa) or a day or so (N. caerulea), partly by being bursted and torn through absorption of water, partly by decay (Fig. 41, b). The seed proper is protected by a firm shell consisting of two parts, the outer a single layer of thick-walled, close-fitting cells, the inner a. D Fio. 41.—The aril. If. a, diagrammatic section of aril and seed; Z>, portion of aril after the seed is dropped; c, cell of the aril where the outer wall bends in, in continuity with the inner wall of the aril; cJ, cell of inner wall; e, cell of outer wall. few layers of thick-walled, but loosely placed cells. The latter layer is of the same thickness as the former ; its cells are much flattened tangen- tially and contain large tangential air-spaces ; the walls are lignified, with the exception of a thin layer next to the lumen. The cells of the outer layer are also strongly compressed tangentially (except in ). On account of the great induration, which is thickest on the outer wall, they have but a small lumen (Fig. 42). The walls are penetrated by pore- canals. They are composed of lignin, excepting a thin layer of cellulose next to the lumen and an outer thin cuticula which projects inward along the boundaries of the cells. In the cells there are (in N. alba) bluish-green granules which give color to the seed. In surface view the outer cells are arranged in longitudinal row
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