632 



PHYSIOLOGY. 



embryo-sac. It is a large cell, filled Fig. 610. 



with watery fluid and protoplasm, and 



contains at its summit the germinal 



corpuscles (e v], globular or oval masses 



of protoplasm, one of which becomes 



the germinal vesicle. 



Some authors assert that these corpuscles 

 are cells "before impregnation; but we hold 

 that they are merely corpuscles of proto- 

 plasm, or rather free primordial utricles 

 (p. 495), like the unfertilized spores of Fucus 

 (p. 443). In fig. 612, A, e v, is shown the 

 condition before fertilization in Santalum. 

 Most observers consider that the germinal 

 vesicles exist before fecundation ; but Tu- 

 lasne inclines to the belief that they are the 

 first results of that process. In some cases, 

 at the bottom of the einbryo-sac, small cells 

 (antipodal cells) have been seen, which are 

 formed before the germinal corpuscles by 

 free-cell formation, have only a temporary 

 existence, and disappear after fertilization. 

 The purport of these cells is not known. 



Embryo-sac. The embryo-sac is usually solitary, but in 

 Crucifers there are several, one of which alone becomes fertilized. 

 It exhibits different modes of development 

 in different Orders of plants. In the 

 OrchidaceaB the cell which constitutes the 

 embryo-sac (fig. 609) very soon oblite- 

 rates the surrounding cells, here a single 

 layer, and comes to form the entire nucleus 

 (c, d, e, /). In the Composite an analogous 

 condition is met with. In the Leguminosae 

 the embryo-sac sometimes expands so much 

 as to cause the absorption of the inner 

 integument even before fertilization. In 

 Gryninosperms the embryo-sac remains sur- 

 rounded by layers of cells belonging to the 

 nucleus till after fertilization has taken 

 place. 



The embryo-sac often only occupies a 

 moderate part of the nucleus (fig. 610), 

 and may then be a simple cylindrical or 

 oval sac, or run out into pouches or diverti- 

 cula, as occurs especially in Scrophulariaceae. 

 A remarkable condition occurs in Santalacese, 



Vertical section of the ovule of the 

 garden Hyacinth, just before 

 impregnation : f, funiculus ; r, 

 raphe ; c, chalaza ; n, nucleus ; 

 , inner integument; p, outer 

 integument ; m, micropyle ; es, 

 embryo-sac ; ev, germinal cor- 

 puscles,one of which gives origin 

 to the embryo. Magn. 25 diam. 



Fig. 611. 



Vertical.section of the ovary, 

 containing one ovule, of 

 Carduus : s, base of the 

 canal of the style ; o, body 

 of the ovule ; pt, bundle 

 of pollen-tubes, descend- 

 ing from the stigma; es, 

 embryo-sac ; e, nascent 

 embryo. Magn. 25 diam. 



