SEED OF PICEA. 



379 



as albumen or endosperm, densely filled with reserve food- 

 materials. It forms a sac, enclosing the embryo. This sac 

 is open at its micropylar end, and here the radicle .of the embryo 

 is situated against the displaced remnant of the nucelms. The 

 embryo can be easily made out in seeds cut in the direction of 

 their length. It looks somewhat cylindrical, gradually getting 

 thicker towards the cotyledonary end. In consequence of being 

 tilled with reserve food-materials it is white, and as opaque as the 

 albumen or endosperm of the seed. 



We prepare a median longitudinal section through the seed 

 between the fingers, and lay it in carbolic acid diluted with 

 alcohol. The figure becomes very beautifully 

 clear, far better than in potash, and even better 

 than in chloral hydrate, so that we can follow 

 every row of cells. We see (Fig. 139) that the 

 cotyledons (c) do not reach quite a third of the 

 whole length of the embryo. At the base between 

 them is to be jseen the growing apex (punctum 

 vegetationis) of the embryonic stem. The stem 

 (caulicle) itself, which is distinguished as the 

 hypocotyl (h) passes, without clear limitation, 

 into the root (the radicle). This is for] the most 

 part represented only by a growing apex, which 

 shows clearly in the interior of the body of the 

 embryo as the apex of the plerome (pi) of the 

 root, while the cell-rows of the cortex (periblem) 

 of the hypocotyl pass directly into the parabolic 

 layers of the root cap (cp), a condition which 

 recurs in all roots of the Gymnosperms, since we 

 can see the cell-rows of the cortex of the body 

 of the root pass over direct into the cell -layers of 

 the root-cap (cf. Thuja, p. 223). The root-cap is 

 traversed in the direction of its long axis by a distinctly-marked 

 column of tabular cells, arranged in straight rows. In the 

 hypocotyl the tissue of the pith (m) already begins to show, and 

 around this the elongated cells of the procambium ring (op), in 

 which the vascular bundles will make their appearance. These 

 cells can be traced, moreover, for a short distance along the 

 median section of the cotyledons (compare the Fig.). Thus 

 in the embryo the essential parts of the future plant are already 

 present. 



FIG. 139. Longi- 

 tudinal section 

 through the ripe 

 embryo, c, cotyle- 

 dons ; h, hypocotyl ; 

 pi, growing apex of 

 the plerome ; cp, 

 root-cap ; d, its 

 central column ; m, 

 pith ; op, procam- 

 bium ring in the 

 hypocotyl (x 10). 



