ANGIOSPERMS. cir 



which is already divided by a longitudinal and a transverse wall into four cells arranged 

 like quarters of a sphere. A comparison of the states //— V shows that the further 

 development advances first of all in a basipetal direction. A cell w or h, the result 

 of intercalary division, which arises between the end of the pro-embryo and the body 

 of the embryo a c already formed, is especially to be noted. It is from this that the 

 root is subsequently developed. Hanstein calls it and the tissue which proceeds 

 from it the Hypophysis. Before the body of the embryo undergoes any external 

 differentiation, its primary meristem separates into a single peripheral layer (shaded 

 in the drawing), and a tissue internal to this ; the former is the primary epidermis or 

 dermatogen, which continues to grow only at the surface 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 oi the 

 embryo, it begins also in the hypophysis h. The lower layer of this hypophysis 

 takes no part in the formation of the dermatogen, while from its upper layer 

 (in VF) 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 first cotyledon, at the base of which h the apex 

 of the stem is afterwards formed laterally. But if the cotyledon is really the 

 apical structure of the embryo, which seems to me to be not yet sufficiently 

 established, it cannot possibly be a foliar structure, 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 embryonic 

 vesicle 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-pas ton's for detailed description. Fig. 372 shows first of all that 

 the mass of the embryo is developed from the spherical apical cell of the pro- 

 embryo V, and in what manner this takes place; here also a basal cell k of the 

 body of the embryo forms the hypophysis, from which the radicle is developed. 

 The spherical primary cell of the embryo divides first by a longitudinal wall i, i 

 (in / — IV), followed in each of the two halves by a transverse division 2, 2, so 

 that the body of the embryo consists at first of four quarters of a sphere, each 

 of which next undergoes another tangential division, by which four outer cells 

 are formed as the rudiment of the dermatogen, and four 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 

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

 produced from the primary cell of the embryo thus increases rapidly by the multi- 

 plication of its cells, and two large protuberances (F, cc), the first leaves or 

 cotyledons, soon make their appearance one on each side of the apex {s) ; the 



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