ITS STRUCTURE AND TARTS. 321 



provided with a tuft of hairs at one end, termed a Coma ; as in 

 Epilobium and Milkweed (Fig. G02). In the Cotton-plant, the 

 whole surface of the seed is covered with long wool. 

 It should likewise be noticed, that the integument of 

 numerous small seeds is furnished with a 

 coating of small hairs containing spiral 

 threads (one form of which is represented 

 in Fig. 44), and usually appressed and con- 

 fined to the surface by a film of mucilage. 

 When the seed is moistened, the mucilage 

 softens, and these hairs spread in every 

 direction. They are often ruptured, and 601 



the extremely attenuated elastic threads they contain uncoil, and are 

 protruded in the greatest abundance and to a very considerable length. 

 This minute mechanism subserves an obvious purpose in fixing 

 these small seeds to the moist soil upon which they lodge, when dis- 

 persed by the wind. Under the microscope, these tlu-eads may be 

 observed on the seeds- of most Polemoniaccous plants, and on the 

 achenia of Labiate and Composite plants, as, for example, in many 

 species of Senecio, or Groundsel. In Peony the testa becomes 

 fleshy or baccate ; in Magnolia it. imitates a drupe. 



628. The inner integument of the seed, called the Tegmen or 

 Endopleura, although frequently very obvious (as in Fig. 599, c), 

 is often indistinguishable from its being coherent with the testa, and 

 is sometimes altogether wanting. 



629. The stalk of the seed, as of the ovule, is called the Fu- 

 niculus (Fig. 600, a). The scar left on the face of the seed, by its 

 separation from the funiculus at maturity, is termed ihe Hiluxi. 

 The chalaza and rhaphe, when present, are commonly obvious in 

 the mature seed, as well as in the ovule (564-568), and the name 

 and relations of these several parts in the seed are the same as in 

 the ovule. Also the terms orthotropons, anatropous, camjyylotropous, 

 •fee, originally applied to the ovules, are extended to the seeds which 

 result from them ; so that Ave may say, Seeds anatropous, as well as 

 Ovules anatropous, &c. 



630. Aril or Al'illllS. Some seeds are furnished with a covering, 

 (usually incomplete and of a fleshy texture,) wholly exterior to their 

 proper integuments, arising from an expansion of the apex of the 



FIG. 601. The winged seed of Trumpet-Creeper. 



FIG. 602. Seed of Milkweed (Asckpioa Cornuti), with its coma or tuft. 



