ORGANS OF EEPRODUCTIOX. 327 



this micropyle is of some practical importance, as the radicle, 

 r, of the embryo, with a few exceptions, is directed towards it. 

 It should be noticed that while the micropyle constitutes 

 the organic apex of the oviile, the chalaza indicates that of the 

 seed. 



The terms orthotropous, campy lotropous, anatropous, &c., are 

 applied to seeds in the same sense as to ovules ; consequently 

 the hilum, chalaza, and micropyle, have the same relations to 

 each other in the seed as in the ovule. Thus the hilum and 

 chalaza are contiguous to each other in an orthotropous seed, 

 and the micropyle is removed to the opposite end ; in a campy- 

 lotropous seed the hilum and chalaza are also near to each other, 

 and the micropyle is brought round so as to approach the hilum ; 

 in an anatropous seed the chalaza is removed from the hilum 

 and placed at the other end, while the micropyle and hilum cor- 

 respond to each other ; while in amphitropous and semi-anatro- 

 pous seeds, the chalaza and micropyle are both removed from the 

 hilum, and placed transversely to it. 



Almost all seeds, like ovules, are more or less enclosed in an 

 ovary, the only real exceptions to this law being in Gymnosper- 

 mous plants, as already referred to under the head of the Ovule ; 

 and hence the division of Phanerogamous Plants, as already 

 noticed, into Gymnosperms and Angiosperms. The means of 

 distinguishing small fruits from seeds have been also already 

 described. (See p. 289.) 



In describing the position of the seed in the ovary, the same 

 terms are used as already mentioned under the head of the 

 Ovule. Thus a seed maybe erect, inverse or pendulous, sus- 

 pended, asctndiyig, &c. The number of seeds contained in the 

 pericarp is also subject to variation, and corresponding terms 

 are used accordingly ; thus we say the pericarp is monospermous, 

 bisjiermous, trispermous, quadrispermous, quinquespermous, mtd' 

 tispermous, &c., or one-seeded, tivo-seeded, three-seeded, four- 

 seeded, five-seeded, many-seeded, &c. 



The seed also varies much in form, and, in describing these 

 variations, similar terms are employed to those used in like mo- 

 difications of the other organs of the plant. Thus, a seed may 

 be rounded, as in the Nasturtium ( fig. 729), ovate, as in Poly- 

 gala {fig. 739), oval, as in Asclcpias {fig. 735), obovate, as in 

 Delphinium {fig. 731),reniform, as in Papaver {fig. 730), «fcc., &c. 



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

 possesses in common with the ovule, we pass to the consideration 

 of its special characteristics. 



Structure of the Seed. — The seed consists essentially of two 

 parts; namely, of a Nucleus or Kirnel {fig. 737, n) and Integu- 

 ments {fig. 737, t). We shall describe each of these parts sepa- 

 rately. 



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



