134 



THE SEED. 



Fig. 262. Seed, 

 a, cotyledons ; b, embryo. 



Acorn (Fig. 261) ; Legumen or Legume, as in the Pea (Fig. 260) ; Siliqua, or pod, as 

 in the Mustard (Fig. 255), and which differs from the Legumen chiefly in the longi- 

 tudinal false dissepiment at a being present in the former, and dividing the cavity into 

 parts ; Capsule, as in the Larkspur (Delphinum] or Poppy (Fig. 254) ; and acca, or two 

 berry, as Currant. 



The Seed. The seed is the mature ovule, and in its internal anatomy maintains 

 a great resemblance to that body. The pro- 

 cess of growth and development has, how- 

 ever, induced certain modifications which it 

 it needful to understand, and the more so 

 that the characters of the seed have of late 

 years become of great importance in the 

 description and classification of plants. Like 

 the ovule it consists, in general terms, of 

 a growing point, and contains membranes. 

 The term embryo is expressive of the former 

 (Fig. 262 ), and testa, in a general sense, of 

 the latter. 



The testa, or coverings of the seed, are divisible into three or more layers viz. the 

 outer one, or primine ; the inner one, or secundine ; and the third coat, or tercine. The 

 detection of these three coats is oftentimes a matter of difficulty ; but our readers who 

 have tolerably good microscopes, and who have attained to a certain degree of delicacy 

 of manipulation, need not fear to enter upon it. It will be needful to examine a seed 

 in its fresh state, and to seek the separation of its coats by immersion in water for some 

 hours, and subsequently by the aid of the needles. 



The outer integument is commonly smooth, somewhat dense, and resisting ; but it 

 may assume every variety of character. The most interesting departure from the 

 established rule is in the instance of the Cotton seed (Gossypium], Sage (Salvia, Fig. 

 263), and the Collomia grandiflora, in which a large number of 

 shrivelled hairs are attached to this membrane. There is no 

 difficulty in seeing them in the Cotton plant under every condi- 

 tion ; but in the latter examples they are inappreciable to the 

 naked eye, until they have been immersed for an instant in 

 water, when they start out, and give a fringed character to the 

 seed. The hair in this case contains a spiral fibre (Fig. 263), 

 which is the cause of its elasticity (pages 14 and 66). In other 

 instances it is largely developed and fleshy. The inner membrane 

 is placed immediately within the outer integument, and itself 

 incloses the most external or third coat. This latter envelope 

 is in immediate proximity to the nucleus or embryo, and is diag. 

 nosed from its inclosing covering simply by the non-perforation 

 of its apex. 



These various membranes are seldom distinct in the seed, and consequently it is 

 customary to speak of the testa of the seed rather than of the primine, or any other 

 specific part of the covering. 



The Nucleus. This is the growing point already referred to at page 129, as the 

 nucleus of the ovule, and now consists of two distinct parts, the true growing point, 

 or embryo, which, in the futiire germination, elongates upwards and downwards to 



Fig. 263. Fibres of 



