5H 



PHANEROGAMS. 



Structures, the cotyledons, subsequently arise, while the rudiment of the first root 

 may be observed in the differentiation of the tissue at the boundary-line of the pro- 

 embryo and embryo. The first cells of the embryo are not unfrequently disposed 

 as if they had resulted from oblique divisions of an apical cell in two or three 

 directions (Fig. 369 C), a supposition which is completely supported by the oblique 

 position of the first septum of the apical cell in the pro-embryo ; in Rheum I also found 

 the apex of young embryos to present an appearance which suggested the existence 

 of a three-faced apical cell. According to Hanstein's new and prolonged researches, 

 the process is, nevertheless, different ; he asserts that the first longitudinal wall, even 



Fig. 371.— Formation of the embryo of Monocotyledons (Alisma) (after drawings by Hanstem) ; I—VIII various stapes 

 of development; v the pro-embryo, h the liypopliysis. iv the region in which the radicle is formed, / the region in 

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

 is shaded). 



when it stands obliquely to the last transverse wall, is still in the median plane of the 

 body of the embryo which is being formed, and is frequently at right angles to the 

 last transverse wall, and therefore in the axis of growth of the pro-embryo \ The 

 formation of this median longitudinal wall in the primary embryonic vesicle com- 

 pletely excludes the possibility of a bi- or pluri-seriate segmentation of the apical cell. 

 We learn from Hanstein that the mode of formation of the embryo of Monocotyledons 

 may be seen remarkably clearly in Alisma. In Fig. 371, //, are shown, above the 

 pro-embryonic cell v, two other cells a and c lying one over the other, the last of 



^ The description in the text is taken from Hanstein's preliminary publications (Monatsberichte 

 der niederrhein. Gesellsch. fur Natur- und Heilkunde, July 15 and August 2, 1869), as well as from 

 more detailed communications in letters. Professor Hanstein has also had the kindness to allow me 

 the sight of a number of drawings; and, with his permission, the figs. 371-374 are copied from 

 them. I have also had the opportunity, in the summer of 1869, of seeing preparations of Hanstein's 

 ^similar to Fig. 372. Compare also Hanstein, Botanische Abhandlungen, Heft I, for a more detailed 

 description of the development of the embryo in Monocotyledons and Dicotyledons. [See also 

 Quart Joum. Micr. Soc. 1873, p. 51.] 



