136 ANATOMY AND PHYSIOLOGY OF 



the pro-em"bryo has been changed into a compound cellnlai* body 

 by successive subdivi&ions. In this process there may be forma- 

 tion merely of cross-walls, so as to change the pro-embryo into a 

 conferYoid, jointed (pi. I, fig. 17, a; 18, a) fiequently elongated 

 row of cells lying one above another (for example, in the Scro- 

 phnJarinese and Cruciferse), or the filamentous pro-embryo may 

 pretty early pass into a mass of cellular tissue by longitudinal 

 division of its cells (for instance, in Statice, TropcBolum^ Zea, Fri- 

 tillaria^ &c.). Whichever takes place, the terminal cell of the 

 whole structure is sooner or later metamorphosed, by preponder- 

 ating giowth and cell-division in diflerent directions, into a cel- 

 lular structure, at first of globular form (pi. 1, fig. 17, &; 1S,b), 

 which, the more fully it becomes developed, the more marked 

 contrast does it present to the other part of the pro-embryo turned 

 towards the micropyle end (called the suspensor, Trager^ or 

 Aufhang&faden), The ulterior development shews that this 

 mass of cells foimed at the end of the pro- embryo is in the rudi- 

 ment of the embryo. It may persist, in plants with the so-called 

 " homogeneous embryo^' (e. g,, in the Orchidese and in Monotroi^a)^ 

 in the form of a globular or elliptical body, composed of a variable 

 number of cells (pi. 1, fig. 1 8) ; but usually the cotyledons shoot 

 out at the end turned away from the suspensor, a little below the 

 actual extremity (in the Monocotyledons in the form of a sheath- 

 ing leaf, in the Dicotyledons in the form of two opposite leaves,) 

 and after this the apex is developed into the terminal bud (^plu- 

 muUf federchen). 



In this way the embryo is always suspended in an inverted 

 direction, with the point of its stem downwards, in the embryo- 

 sac. Its radical extremity, as is evident from the mode of origin 

 of the embryo, is not free, but blended with the cells of the pro- 

 embryo ; frequently it does not at once become clearly distin- 

 guishable from the cells of the pro-embryo, but the line of de- 

 marcation becomes continually more definite with the advancing 

 development, since the cells of the embryo are always densely 

 filled with organic matters, while the cells of the suspensor -usually 

 contain only a little opake sap, and are thus far more transparent 

 than those of the embryo, fi:om which they are also fi^equently 

 distinguishable by much greater si^e. The further the develop- 

 ment of the embr;^ o progresses, the more, in most cases, does vege- 

 tation cease in the cells of the suspensor, so that, if even, as in the 

 Orchidese, it still exil)its a considerable growth during the deve- 

 lopment of the embryo, and exists when the seed is ripe, it at all 

 events forms but a dead, readily detachable appendage of the 

 radicle, upon the embryo of the ripe seed. 



The origin of the embryo, which is formed out of a cell of the 

 pro-embryo, and liot free in the cavity of the embryo-sac, bears great 

 resemblance to the formation of a bud, and especially to the for- 

 mation of the stem-producing buds developed on the pro-embryo of 



