ITS STRUCTURE AND PARTS. 



321 



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

 Epilobium and Milkweed (Fig. 602). In the Cotton-plant, the 

 whole surface of the seed is covered with long wool. 

 It should likewise he 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 

 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 threads may be 

 observed on the seeds of most Polemoniaceous plants, and on the 

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

 species of Senecio, or Groundsel. Li 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 the ITilum. 

 The chalaza and rhaphe, when pi'esent, 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 orthotropous, anatropous, campylotropous, 

 &c., originally applied to the ovules, are extended to the seeds which 

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

 Ovules anatropous, «fec. 



630. Aril or Arillus. 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 (Asclepias Cornuti), with its coma or tuft. 



