OVULES OF AKGIOSPEEMIA. 



631 



which layer is absorbed as the ovule grows (c, d), so that the embryo-sac 

 constitutes the whole nucleus of this ovule. In a the inner integument 

 partially encloses the nucleus ; in b the outer integument has grown up 

 over this to a certain extent; and both are still more developed in c, 

 where the inner coat has covered up the nucleus (leaving the endostome, 

 p. 137), but itself projects from the outer coat. In d the outer coat has 



Fig. 608. 



Fig. 609. 



o 



Fig. 603. Ovules, showing gradual formatiou of coats over the nucleus and progressive cur- 

 vature. 



Fig. 609. Development of the ovule of Orchis Morio : o, a young ovule, with the nucleus 

 projecting from the inner coat ; b, an older ovule becoming anatropous, with the 

 outer coat growing up over the inner ; c, section of a more advanced ovule ; d, 

 section of an ovule with the pollen-tube (pt) passing down the micropyle, and 

 in contact with the embryo-sac ; f, an embryo-sac extracted, with three germinal 

 corpuscles ; g, another, with the end of a pollen-tube adherent. Magn. about 

 100 diam. 



grown up over the inner, and the micropyle or foramen (p. 137) consists 

 of a wide exostome and a narrow endostome, into which the pollen-tube 

 (p t) has penetrated. 



Ovules are seldom so small, or composed of so few cells, as the fore- 

 going; more frequently the nucleus is a cellular mass of some size, and 

 the coats are composed of several strata of cells. The outer coat is the 

 primine, the inner the secundine, of Mirbel. 



At the epoch when the pollen is scattered from the anthers, the 

 ovule presents the characters which are illustrated in fig. 610, 

 which represents the anatropous ovule of the garden Hyacinth. 

 The nucleus (fig. 610, n) is surrounded (in this case) by two coats 

 (s & p\ which are perforated above by a canal, the micropyle (m) ; 

 at the base of the nucleus is the chalazal region (c), whence the 

 integuments (s & p) arise, and where the raphe (r) 9 with its spiral 

 vessels, ends. In the centre of the nucleus is a long sac (e s), the 



