64 SUilMAEY OF CUKEENT RESEARCHES RELATING TO 



BOTANY. 



A. GENERAL, including Embryology and Histology of the 

 Phanerogamia. 



Origin of the Embryo-sac and Functions of the Antipodal 

 Cells.* — After referriug to the views on these subjects already pub- 

 lished by Warming, Vesque, Strasburger, Fischer, Ward, and Treub,t 

 L. Guignard details a series of observations of his own on a variety of 

 plants, to determine some of the controverted points. 



As a type of the Mimosete, in which the phenomena are remark- 

 ably uniform, he takes Acacia retinoides. At the summit of the 

 nucellus, beneath the epidermis, an axial cell, somewhat larger than 

 the adjoining ones, divides into two superposed cells ; one, the origin 

 of the cap (^calotte) in Dialypetalfe, in immediate contact with the 

 epidermis ; the other Warming's primordial mother-cell of the embryo- 

 sac, situated at a greater depth ; these he calls the apical and sub- 

 apical cells. The apical cell gives birth to a tissue which is generally 

 reduced to three broad cellular layers. The subapical cell rapidly 

 enlarges, and becomes segmented horizontally in the basijoetal direc- 

 tion, dividing thus into three superposed cells each equal in size to 

 the mother-cell. Of these the lowest is alone the true mother-cell of 

 the embryo-sac, enlarging at the expense of the others and of the 

 lateral nucellar tissue. The nucleus increases in size, and becomes 

 surrounded at first by granular protoplasm, then by grains of starch, 

 which finally often entirely fill up the cell-cavity. Eesorption soon 

 commences in the two superposed cells ; their nuclei lose their sharp 

 outline, the cell-walls disappear, and the entire protoplasm has the 

 appearance of a homogeneous and refractive mass, the nuclei be- 

 coming indistinguishable ; finally the whole substance of these cells 

 is absorbed in the development of the lower mother-cell. 



This process is subject to certain variations ; but it is always the 

 lower cell which becomes the mother-cell, and absorbs the others. 

 The starch-grains disappear during the formation of the eight nuclei 

 which give rise to the synergidas, the oosphere, the antipodal cells, 

 and the two polar nuclei which coalesce in order to form the secondary 

 nucleus of the embryo-sac. 



In the CfBsalpinieae the apical cell generally gives rise to a thick 

 tissue which remains for a considerable time, even after impregnation. 

 Variations occur in the subsequent development ; and these are 

 greater among the Papilionacese, not only in genera of the same tribe, 

 but even in species of the same genus. In this order the apical cell 

 gives rise only to two superposed cells ; the subapical cell remains 

 undivided, increases early, and displaces the others. 



As a general result, whatever may be the differences in the origin 

 and number of the cells which constitute the axial row of the nucellus, 

 it is the inferior cell only which is the true mother-cell of the embryo- 



* Bull. Soc, Bot. France, xxviii. (1881) pp. 197-201. 



t See this Journal, ii. (1879) p. 903; iii. (1880) pp. 107, 979; i. (1881) pp. 

 260, 620. 



