59° 



PHANEROGAMS. 



dermatogen, which continues to grow only in extent and divides only in a radial 

 direction; the figures IV — VI show that the dermatogen is marked off from the 

 primary cells of the embryo by tangential divisions proceeding towards the base. 

 The inner mass of tissue soon undergoes further differentiation ; an axial string of 

 tissue is produced by divisions, especially longitudinal, forming the plerome or tissue 

 which subsequently produces the fibro-vascular bundles ; the primary meristem lying 

 between the plerome and the dermatogen, and which undergoes copious transverse 

 divisions, is the periblem, /. e. the primary cortical tissue. At the same time that 

 this differentiation of tissue is first indicated in the upper part a c of the embryo, 

 it begins also in the hypophysis k. The lower layer of the hypophysis takes no 

 part in the formation of the dermatogen, while from its upper layer (in VI) is 

 formed a prolongation of the dermatogen and of the periblem of the body of the 

 embryo, from which, as will be explained further on, the root is developed as a 

 posterior appendage of the embryo. Hanstein designates the apical part c of the 

 embryo the cotyledon, at the base of which d the apex of the stem is afterwards 

 formed laterally : the cotyledon is apparently developed from the cells c in //, the 

 apex of the stem and its hypocotyledonary portion (hypocotyl) together with the 

 upper part of the primary root from the cell a in //. But if this apical part is 

 really the cotyledon, which seems to me to be not yet sufficiently established, the 

 cotyledon cannot possibly be a foliar structure (phyllome), even if (as in Allium) 

 it subsequently assumes altogether the appearance of a foliage-leaf. 



The different stages in the development of the embryo from the oospore are 

 much more clearly seen in Dicotyledons than in Monocotyledons, the Grasses in 

 particular among the latter presenting difficulties. Hanstein has singled out Capsella 

 Bursa-pastoris for detailed description. Fig. 403 shows first of all that the mass 

 of the embryo is developed from the spherical apical cell of the suspensor v^ and 

 in what manner this takes place; here also a cell h of the suspensor forms the 

 hypophysis which contributes to the formation of the primary root (radicle). The 

 spherical primary embryo-cell divides first by a longitudinal wall i — i (in / — IV)\ 

 [each of the two cells thus formed is then divided into two by a longitudinal wall at 

 right angles to the first, so that the embryo now consists of four cells which are 

 quadrants of a sphere ;] this is followed in each of the quadrants by a transverse 

 division 2 — 2, so that the body of the embryo now consists of eight cells (octants 

 of a sphere), each of which next undergoes a tangential division, by which eight 

 outer cells are formed as the rudiment of the dermatogen, and eight inner central 

 cells (//). While the first only multiply by radial divisions, the inner mass of tissue 

 grows in all directions, resulting at an early period in its differentiation into plerome 

 (///, /F, F", shaded in the drawing) and periblem. The mass of tissue which is 

 produced from the primary embryo-cell thus increases rapidly by the multiplication 

 of its cells, and two large protuberances (F, <: r), the first leaves or cotyledons, soon 

 make their appearance one on each side of the apex {$) ; the apex of the stem 

 exists for the present only as the end of the longitudinal axis of the embryo ; an 

 elevated mass of tissue, the vegetative cone of the stem, is not formed till later, deeply 

 enclosed between the cotyledons. The posterior or basal end of the axis of the 

 embryo after the differentiation of its primary meristem into dermatogen, periblem, 

 and plerome (//, ///, IV), is, so to speak, open, as long as this differentiation 



