ANGIOSPERMS. 



589 



the embryo-cell completely excludes the possibility of a bi- or pluri-seriate seg- 

 mentation of the apical cell. We learn from Han stein that the mode of formation 

 of the embryo of Monocotyledons may be seen remarkably clearly in Alisma. In 

 Fig. 402, //, are shown, above the suspensor v, two other cells a {a is formed 

 by the division of the cell v in I) and c lying one over the other, the last of which 

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

 like quadrants of a sphere. A comparison of the stages //-— V shows that the 

 further development advances first of all in a basipetal direction. A cell w or k, 

 the result of intercalary division, which arises at the end of the suspensor next to 

 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 



Fig. 402. — Formation of the embryo of Monocotyledons (Alisma) (after drawings by Hanstein) ; / — VIII various 

 stages of development ; v the suspensor, /* the hypophysis, w the region in which the radicle is formed, / the region in 

 whicn the plumule is formed, c cotyledon, b first leaf (VII and VIII much less magnified than the rest ; the dermatogen 

 is shaded). / consists of the rudimentary suspensor v, and of the embryo- cell. 



differentiation, its tissue differentiates into a single peripheral layer (shaded in the 

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



to the recent literature of the subject: Fleischer, Beitr. zur Embryologie der Monokotylen und 

 Dicotylen, Flora, 1874. — Hegelmaier, Zur Entwick. monokotyledoner Keime, Bot. Zeit. 1874; id. 

 Vergl. Untersuch. lib. Entwick. dikotyledoner Keime, mit Beriicksichtigung der pseudo-monokotylen, 

 Stuttgart, 1878. — Solms-Laubach, Ueb. monocotyle Embryonen mit Scheitelbiirtigem Vegetations- 

 punkt, Bot. Zeitg. 1878. — Treub, Sur I'embryogenie de quelques Orchidees, Amsterdam, 1879. — 

 Westermaier, Die ersten Zelltheilungen im Embryo von Capsella Bursa pastoris. Flora, 1876. — 

 Famintzin, Embryologische Studien, Mem. de I'Acad. Imp. de St. Petersbourg, ser. 7, t. XXVI, 

 1879.] 



^ [According to Famintzin, the cell w or h is derived, not from the suspensor, but from the 

 division of the cell a : this being the case, it is tlie cell a which must be regarded as the hypophysis. 

 If this is so, the hypophysis, in Alisma, contributes more largely to the formation of the embryo 

 than in other instances. Possibly this explanation may be applied to all cases in which two 

 embryo-cells are said to be present.] 



