THE OVULE AND EMBRYO-SAC. 



373 



longitudinal 

 re- 



nc 



fruit -scale with the points of the needles. We prepare longitudi- 

 nal sections of it between thumb and forefinger, but as the 

 integument has become comparatively hard we must somewhat 

 modify our method of preparation. We cut the ovule in two with 

 the scissors at about its mid height ; we then take the upper half 

 of the ovule, i.e., that which contains its apex, between the 

 fingers, and with the forceps withdraw the nucellus out of the cut 

 surface. Through this 

 longitudinal sections can 

 now be readily made. 

 We examine in glycerine. 

 We first, however, 

 examine a 

 section of an entire 

 ceptive ovule with a low 

 power. The entire ovule, 

 with integument, is cut 

 perpendicularly to its sur- 

 face of insertion ; it is 

 displayed, therefore, in 

 median longitudinal view 

 (Fig. 136). We see in 

 it the integument (/), 

 which develops into the 

 skin of the seed, and from 

 mid-height is separated 

 from the nucellus ; the 

 nucellus, bearing upon 

 its apex pollen-grains, 

 which partly are external, 

 anrl rmvtlv KP -nnt in itc FlG - 136. Median longitudinal section through 

 and paitlj lie sunk in Its a rece ptive ovule of Picea vulgaris, Lk. e, embryo- 

 tissue ; or mav even show sac nlle( i witl endosperm ; , ventral portion, and 



c, neck of an archegoniuru ; n, the nucleus of the 

 pollen - tubes (t), de- oosphere ; nc, the nucellus of the ovule ; p. pollen- 



vplrmprl frnmtViPQPnnllpr. raius U P OU aud iu the uucellar a P ex fc pollen- 



tubes, traversing the nucellus ; i, integument ; s, 

 grains, which penetrate the wing of the seed(x 9). 



the upper part of the 



nucellus, in order to reach the external layer of the embryo-sac ; 

 the embryo-sac (e), of elliptic outline, filled with endosperm (or 

 more correctly, prothallium tissue) ; the archegonia, known 

 formerly as corpuscula, whose ventral portion (a) is easy, but 

 neck more difficult, to recognise ; in the interior of each arche- 



