ORGANS OF REPRODUCTION. 337 



as in Delphinium (fig. 728), reniform, as in Papaver {fig. 1'21\ 

 &c., &c. 



Having now allnded to those characters, &c., which the seed 

 possesses in common with the ovule, we pass to the consider- 

 ation of its special characteristics. 



Structure of the Seed. — The seed consists essentially 

 of two parts; namely, of a Nucleus or Kernel {fig. 725) and 

 Integuments {fig. 725, te and e), &c. We shall describe each of 

 these parts separately. 



1. The Integuments. — There are usually two seed-coats or 

 integuments, which have been variously named by different 

 botanists. The terms most frequently used, are testa or episperm 

 for the outer coat ; tegmen or endopleura for the inner ; and 

 sj)ermoderm for the two when spoken of collectively. Some 

 writers, however, use the word testa in a general sense for the 

 two integuments, and call the external one spermodemi. The 

 names first mentioned, are those Avhich will be used in this 

 volume. Some botanists, again, describe a third integument 

 under the ' name of sarcoderm ; this layer, however, is com- 

 monly and more accurately considered, as but a portion of the 

 outer integument, in which sense we understand it here. 



a. Testa, episperm, or outer integument {fig. 725, te). This 

 integument may be either formed of the primine of the ovule 

 only, or by a union of both primine and secundine, which is 

 more frequently the case. The testa is generally composed of 

 ordinary parenchymatous cells, but in some seeds, Ave have in 

 addition, a coating of hair-like cells containing spiral threads, 

 which are pressed closely to the surface of the seed by a layer 

 of mucilage. (See p. 47.) If such seeds be moistened with 

 water, the mucilage which confines these hair-like cells to the 

 surface of the testa becomes dissolved, by which they are set 

 free, and then branch out in every direction. It frequently 

 happens, also, that the membrane of the cells is ruptured, and 

 the elastic threads which they contain also uncoil, and extend 

 to a considerable distance from the testa. The seed of the 

 Collomid, and many other Polcmoniaceous Plants, &c., exhibit 

 this curious structure; hence they form beautiful microscopic 

 objects. 



Colour, Texttire, and Surface of the Testa. — In colour, the testa 

 is generally of a brown or somewhat similar hue, as in the 

 Almond, but it frequently assumes other colours; thus, in some 

 Poppies it is white, in other species of Poppy, in Indian Shot 

 {Canna), and P^eony it is blackish, in the Arnatto and BaiTicarri 

 {Adenanthera) it is red, in French Beans and Castor Oil it is 

 beautifully mottled, and in the seeds of different plants various 

 other tints may be observed. 



The testa also varies in texture, being either of a soft nature, 

 or fleshy and succulent, or more or less spongy, or membranous, 

 z 



