226 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to the cell-wall. Attention is also directed to the observation of the 

 passage of protoplasm through the cell-wall when the latter has not 

 been swollen by reagents. In these cases thin sections of fresh 

 material were at once treated with saturated picric acid, washed with 

 alcohol, and stained with aniline blue. 



Development of the Embryo of Ruppia and Zannichellia.* — 

 N. Will has examined the history of development of the embryo in 

 these exceptional genera. 



In Buppia rostellata the synergidte of the moderately large and 

 somewhat S-shaped embryo-sac are comparatively small, and soon dis- 

 appear. After impregnation the ovum-cell divides by a septum into 

 two cells, an upper small one, the future embryo, and a lower one, the 

 suspensor, which soon increases considerably in size, but without 

 dividing. The embryo-cell first divides transversely ; the lower of 

 the two cells thus formed then divides longitudinally, as the other one 

 also does later. Each of these four cells then again divides longitu- 

 dinally; so that the embryo now consists of eight cells, and soon 

 afterwards of sixteen. After this an epidermis or dermatogen is dif- 

 ferentiated at an early period. In this stage the embryo consists of a 

 roundish ellipsoidal body, from the upper end of which the cotyledon 

 soon projects. In the depression beneath this is formed the second 

 leaf, and on the ventral side of this latter the third leaf, or perhaps 

 the stem. The cotyledon envelopes the plumule like a sheath. No 

 primary root resembling that of most angiosperms is present, or only 

 a very rudimentary one. In its place a secondary root is formed at 

 an early period, at the base of the cotyledonary sheath on the ventral 

 side, and this root has an exogenous origin. 



The development of Zannichellia palustris agrees more nearly with 

 that of normal monocotyledons. As in Huppia, the impregnated 

 ovum-cell divides first of all into two cells, of which the upper one 

 again divides by a septum. But here the similarity to Buppia ceases. 

 The two upper cells are again divided by septa, and the upper of 

 these two again divides into four cells by two intercrossing longitudinal 

 walls. Septa then make their appearance, and similar divisions take 

 place later in the lower cell. At this stage the embryo consists of 

 seventeen cells, twelve of them in three layers, then two, which later 

 form a similar layer, then one cell, which subsequently divides and 

 apparently forms the root-cap, one cell which becomes the upper 

 portion of the suspensor, and finally the lower part of the original 

 ovum-cell. Subsequently the suspensor consists of two rows of cells. 

 The cotyledon is formed at an early period, inclosing the first leaves 

 of the plumule like a sheath. The tigellum is very thick and con- 

 siderably swollen below. Zannichellia possesses a primary root. 



The author is of opinion that the lower thickened part of the 

 embryo of Buppia is a reservoir of reserve food-material, and that the 

 primary root is aborted, and replaced by an exogenously developed 

 secondary root. 



* Videnskab. Meddelelser fra den naturhist. Forening i Kobenhavn (2 pis.), 

 1882. See Bot. Centralbl., xii. (1882) p. 227. 



