330 SEED OR MATURE OVULE. 



in fig. 577, where / is the funiculus, r the raphe united to the hilum, 

 and chalaza, c, whence vessels, n, penetrate the seed. In some seeds, 

 as Narthecium ossifragum, the vessels are said not to appear tUl after 

 fertilisation, and in Habenaria viridis none have been detected. The 

 chalaza is often of a dififerent colour from the rest 

 of the integuments. In the Orange it is of a reddish- 

 brown colour, and is easily recognised at one end of 

 the seed when the integuments are carefully removed. 

 Sometimes, however, its structure can only be recog- 

 nised by careful dissection. It indicates the cotyle- 

 donary extremity of the embryo. The hilum and 

 Pig. 680. chalaza may correspond, or they may be separated 

 from each other and united by the raphe (fig. 580). The raphe is 

 generally on the side of the seed next the ventral suture.' 



The positions of the hilum, micropyle, and chalaza, are of importance 

 in determining the nature of the seed. The hilum is the base of the 

 seed, and the micropyle its apex, while the chalaza is the organic base 

 of the nucleus. The hilum and chalaza may correspond, the micropyle 

 being at the opposite extremity, and then the seed is orthotropal (ogSoi, 

 straight). The seed may be curved so that the micropyle is close to 

 the hilum, and the chalaza, by the growth of the seed on one side, may 

 be slightly removed from the hilum, then the seed is campylotropal 

 (xafi^'ri'Kog, curved). The micropyle may be close to the hilum, and 

 the chalaza in the progress of development may be removed to the 

 opposite end, then the seed is anatropal (avargs'Tna, I reverse).* 



The position of the seed as regards the pericarp resembles that of 

 the ovule in the ovary, and the same terms are applied — erect, ascend- 

 ing, pendulous, suspended, curved, etc. (figs. 459, 460, 461, 462, 456, 

 pp. 257, 255). These terms have no reference to the mode in which 

 the fruit is attached to the axis. Thus the seed may be erect while 

 the fruit itself is pendent, in the ordinary meaning of that term. The 

 part of the seed next the axis or the ventral suture is its face, the 

 opposite side being the hack. Seeds exhibit great varieties of forms. 

 They may be flattened laterally, compressed; or from above downwards, 

 depressed. They may be round, oval, triangular, polygonal, rolled up 

 like a snaU, as in Physostemon; or coUed up like a snake, as in 

 Ophiocaryon paradoxum. 



The object of fertilisation is the formation of the embryo in the 

 interior of the seed. In general, one embryo is produced, constituting 

 what is denominated monembryony (fiSvog, one) ; but in ConiferiB, 

 Cycadaceae, Mistleto, etc., there are frequently several embryos, giving 



Hg, 580. Seed of the Hazel. /, Funiculus, r, Baphe. c, Chalaza. n. Veins spreading 

 in a radiating manner over the integuments of the seed. 



* See pp. 266, 266, where these terms are more fully explained when treating of the ovule. 



