ITS COATS AND APPENDAGES. 



307 



d 



uated long threads (spiricles) which were coiled within. These, 



protruding in all directions and in immense numbers, form a 



limbus of considerable size around the seed, and evidently must 



serve a useful end in fixing these sma 1 ! 



and light seeds to the soil in time of 



rain, or to moist ground, favorable to 



germination. In cress and flax-seed, 



the abundant mucilage developed when 



wetted comes from the gelatination of 



epidermal cell-walls, and 



subserves a similar use. 



594. While the testa in 

 many seeds is hard and 

 crustaceous or boiry, imitat- 

 ing the pericarp of a nut, in others (such as Paeonia) it becomes 

 berry-like (baccate), and in Magnolia, drupaceous. 1 (Fig. 668- 

 671.) These may also be regarded as adaptations for dissemi- 



672 



nation, here b}- the agency of birds, attracted ~by bright coloring 

 and edible pulp. 



595. The rhaphe of an anatropous seed (shown in Fig. 681, 

 685) is sometimes so salient as to form a conspicuous appen- 

 dage, as in Sarracenia, Fig. 672. Again it may be wholly 



1 See article On the Structure of the Ovule .and Seed-coats of Magnolia, 

 in Jour. Linn. Soc. ii. 100, from which the accompanying figures and Fig. 

 589-597 are reproduced. 



FIG. 668. Forming seed (one eighth of an inch long) of Magnolia Umbrella; the 

 rhaphe toward the eye. GG9. Magnified view of the same divided lengthwise through 

 the rhaphe; the outer coat, a. beginning to form a hard inner layer. n f . Within and 

 distinct from this is the inner coat (l>\ immediately enclosing the nucleus, c. The oppo- 

 site side of the testa is thicker on account of the rhaphe, in which d indicates the cord 

 of spiral ducts. 



FIO-. 670. A nearly full-grown seed, of the natural size 671. Longitudinal section, 

 enlarged, snowing the crustaceous or stony inner stratum of the testa well developed: 

 the parts lettered as in Fig. C>G!>. 672. A transverse section in the same position. 



