^88 PHANEROGAMS. 



[A row of cells is thus formed, from the lowermost of which, usually a spheroidal 

 cell which we may term the embryo-cell, the greater part of the embryo is in most 

 cases formed; but in many cases (in many Papaveracese and Caryophyllaceae, in 

 Asclepias, Cuscuta, Nicotiana, Viola, and others, amongst Dicotyledons, and com- 

 monly among Monocotyledons) the two end cells of the row form the chief part 

 of the embryo. Hanstein considered that the presence of two embryo-cells was 

 characteristic of Monocotyledons, but Hegelmaier has found that a single embryo- 

 cell occurs in this group {e.g. Orniihogalum natans), and that two embryo-cells 

 frequently occur in Dicotyledons, as mentioned above. The upper cells of the 

 row form the Suspensor. In some cases {Glaucium) the cells of the suspensor 

 undergo longitudinal divisions, and it consists consequently of several rows of cells. 

 Usually the lowest cell of the suspensor, the hypophysis, contributes to the forma- 

 tion of the embryo. In the Gramineae the cells of the suspensor divide and form 

 a multicellular appendage at the radicular end of the embryo {Keimanhang, Han- 

 stein) ; when the primary root begins to elongate this mass of cells is split off and 

 it forms a sort of sheath {coleorhiza) to the young root.] The suspensor usually 

 remains short (Fig. 400) ; sometimes, as in Funkia, its basal cell swells up into a 

 globular form (Fig. 399); in other cases (as, according to Hofmeister, in Loranlhus) 

 the oospore lengthens before division, and penetrates to the considerably enlarged 

 base of the long tubular embryo-sac. In those Dicotyledons where the endosperm 

 is formed only at certain lower parts of the embryo-sac by division, a similar elon- 

 gation of the oospore is usual, although not to so great an extent {e.g. Pedicularis, 

 Catalpa, Labiatae). In the embryo-cell a longitudinal or only slightly oblique 

 division-wall first of all makes its appearance, indicating the commencement of the 

 formation of the embryo (see also Fig. 15, p. 18). As this is followed by rapidly 

 repeated divisions, a spherical or ovoid mass of small-celled tissue is produced, from 

 which the first foliar structures, the cotyledons, subsequently arise, while the rudi- 

 ment of the first root may be observed in the differentiation of the tissue at the 

 boundary-line of the suspensor 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. 400 C), a supposition which is com- 

 pletely supported by the oblique position of the first septum in the embryo-cell; 

 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 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 suspensor \ The formation of this median longitudinal wall in 



^ 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. 402-405 are copied from 

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

 similar to Fig. 403. 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. The following are some of the more important contributions 



