758 



PHYSIOLOGY. 



base of the secondary embryo-sacs (^fig. 1111 b, a). These, 

 after fertilization, by the contact of the pollen-tube with the upper 

 end of the sac {pt), become cells, multiply, and form a cellular 

 mass, the lower cells of which break out through the bottom 



Fig, nil. 



Fig. 1111. Development of the embryo in a species of Pimis (Coni ferae). After 

 Henfrey. a. Upper part of the embryo-sac, with two secondary embryo- 

 sacs, corpuscula, or archegonia. B. The same, more advanced, pf. Pollen- 

 tube in the canal leading down to the corpuscula. a. Germinal corpuscles 

 at the base of the secondary embryo-sac. C. Four cellular filaments or 

 sus2)ensors, which are developed from the germinal corpuscles after im- 

 pregnation. D. One of these suspensors, with the embryo (em) at its 

 apex. 



of the endosperm, and grow as four cellular filaments (c), into 

 the substance of the lower part of the nucleus of the ovule ; at 

 the ends of these filaments, cell-division again occurs (d), and 

 from the apex of one of these filaments (suspensois), is de- 

 veloped the embryo (d, em). As there are several corpuscles, 

 and each produces four suspensors, a large number of rudimen- 

 tary embryos are developed; but usually only one of all these 

 rudiments is perfected. The embryo which is fully developed, 

 gradually increases in size, and most of the structures above 

 described disappear, so that the ripe seed exhibits a single em- 

 bryo, imbedded in a mass of endosperm or albumen, the latter 

 originating apparently from the nucleus of the ovule." 



2. Ileproduction of Angiospermia. — The structure of the 

 pollen-grains of the Angiospermia have been already described, 

 (see Pollen, and p. 756), and need nOt be further alluded to 

 in this place. 



The ovule has also been particularly noticed, and we shall 

 now only recapitulate its component parts at the time Avhen the 

 pollen is discharged from the anthers, — that is, just before im- 

 pregnation takes place. It tlien consists of a cellular nucleus 

 (Jig. 1112, n), enclosed generally in two coats, as in the present 

 figure. Sometimes there is but one coat (Jig. 717), and in 

 rare cases the nucleus is naked, or devoid of any coat (^fig. 715). 



These coats completely invest the nucleus except at the 

 apex, where a small opening or canal is left, termed the mi- 



