378 XXVII. REPRODUCTION OF GYMNOSPERMS. 



sac-wise, and adds to the embryonal tubes, so that the " sus- 

 pensor " formed from these becomes more and more massive. 

 The rudimentary embryo itself assumes a cylindrical form, be- 

 comes opaque, and is then very sharply contrasted with the 

 transparent suspensor. When the opaque portion has attained 

 a length of about O5 mm., the rudiment of a root can (after the 

 use of potash, creosote, or chloral hydrate has made it trans- 

 parent) be made out in its interior. This is differentiated at 

 about 0'15 mm. distance from the apex and always by periclinal 

 divisions within a layer of hemispherically-arranged cells (Fig. 

 138, B). Henceforth this root apex adds to the length of the 

 embryonic axis posteriorly by its growth. Soon the other end of 

 the embryonic axis bulges in its middle portion (B), in order 

 to form the growing apex of the stem. Around this then arise 

 in considerable number the rudiments of the seed-leaves or cotyle- 

 dons (C, D and _J). All the parts of the embryo are now 

 present, and need only to grow in order to attain the structure 

 visible in the ripe seed. 



Thus far we have concerned ourselves solely with the most 

 strongly-developing embryo, which ultimately is alone present ; 

 but in reality several, if not all, of the archegonia give rise to 

 rudimentary embryos. All these rudiments grow back into the 

 long axis of the body of the prothallium ; that one, however^ 

 which originates before the others, and first, therefore, makes 

 use of the food-materials stored in the tissue of the prothallium, 

 develops more strongly, and ultimately supplants all the others. 

 At the time when the cotyledons show themselves, the rudi- 

 mentary embryo already lies with its apex at the base of the 

 embryo-sac. With further growth the root end must now be again 

 extended backward, and ultimately attains the position whence 

 the whole development started. The suspensor is pressed up- 

 wards, and ultimately reduced to a knot of disordered cells. The 

 individual cell-rows constituting it separate easily from one 

 another (C). 



The Seed. The seed ripens in October. It then easily 

 separates from the fruit-scale, together with the wing which is 

 developed on the inner side of the seed, leaving behind upon this 

 fruit-scale, after separation, a corresponding hollow. The cells of 

 the spermoderm are, as cross and longitudinal sections readily 

 show, thickened almost to the obliteration of their cavity. A 

 portion of the tissue of the prothallium remains in the seed,. 



