REPRODUCTION OP ANGIOSPERMIA. 



759 



cropyle {Jig. 1112, m). In the interior of the nucleus, but of 

 various sizes in proportion to it, the embryo-sac {Jig. 1112, s) is 

 commonly seen. This sac is, however, liable to many modi- 

 fications; thus, in some cases, as in the Orchidacece {Jigs. 1113 

 and 1114), the embryo-sac completely obliterates the cells 

 of the nucleus by its development, so that the ovule consists 



Fig. 1112. 



Fig. 1113. 



Fig. 1114. 



Fig. 1112. Vertical section of the orthotropous ovule of a species of Polygonum. 

 ch. Chalaza. n. Nucleus invested by two coats, tn. Micropyle. s. Em- 

 bryo-sac. c. Germinal vesicle, or corpuscle Fig. 1113. The ovule, some 



time before fertilization, a. The outer coat. b. The inner coat. s. The 



embryo-sac, with three nuclei at the upper end Fig. 1114. The in- 



!^ ternal parts of the ovule a short time before fertilization, a. Inner coat of 

 the ovule, s. Embryo-sac. 6. Germinal vesicle. After Hofmeister. 



simply ,of it and its two proper coats {Jig. 1113, a, 6). In the 

 Leguminosce, the embryo-sac increases still further, and causes 

 the absorption of the secundine or inner coat of the ovule also, 

 so that it is then simply invested by one coat (primine) ; while 

 in other plants, as in the Santalacea, the sac elongates so much 

 at the apex as to project out of the micropyle. The embryo- 

 sac contains at first a more or less abundant quantity of proto- 

 plasm; in this nuclei aftenvards appear {fig. 1113, s), which by 

 the process of free-cell development, form a corresponding 

 number of cells (usually three), which are commonly termed 

 germinal vesicles {Jigs. 1112, c, and 1114, b). The vesicles are 

 situated at or near the summit of the embryo-sac {Jigs. 1112, c, 

 and 1114, b). Henfrey says, that these are not perfect vesicles 

 with a cellulose coat before impregnation, but merely corpuscles 

 of protoplasm, or rather free primordial utricles hke the unferti- 

 lized spores of Fucus (p. 751). Hence he terms them germinal 

 corpuscles, and applies the term germinal vesicle only to the 

 impregnated corpuscle or rudimentary embryo. "Whether these 

 are simply cori^uscles of protoplasm or true vesicles is therefore 

 doubtful ; but we shall in future, in accordance with the majority 

 of writers, consider them as true vesicles before impregnation. 



Such is the general structure of the unimpregnated ovule. 

 Much difference of opinion has, until lately, existed amongst 



