REPRODUCTION, VEGETABLE (VEGETABLE OVUM). 



106. Hippuris vulgaris.* The already ana- 

 tropous ovule of this plant consists of a cylin- 

 drical nucleus of delicate cellular tissue, along 

 one side of which is observed a longitudinal 

 fleshy ridge, terminating above in a short funi- 

 culus, by which the ovule is suspended from 

 the apex of the one-celled ovary. One of the 

 central cells of this nucleus becomes larger 



Fig. 190. 



249 



into a tubular superior, and a spheroidal and 

 much smaller inferior compartment. The 



Section of naked nucleus of Hippuris vulgaris at an 



early stage, about 16U diam. 



The embryo-sac is seen as a large central nucleated 

 cell. (Unger.) 



than the rest, from which it is further distin- 

 guished by its containing a free vesicular nu- 

 cleolated cell-nucleus and granular fluid. This 

 cell, the embryo sac, rapidly enlarges, and at 

 the same time assumes an elongated oval form. 

 A number of vesicles of various size are de- 

 veloped at the same time, at its micropyle 

 extremity, all of which disappear some time 

 before the scattering of the pollen. Shortly 

 after this has taken place several new cells 

 are formed, one of which, situated towards 

 the upper end of the sac, begins at once to 

 lengthen, and is finally converted into a 

 tube closed at both extremities (germ-cell). 

 The rest arrange themselves in vertical series, 

 so as to form a continuous tissue (the endo- 

 sperm), which completely occupies the lower 

 part of the sac. After this, in consequence, as 

 may be presumed, of the contact of the pollen 

 tube with the membrane of the sac, the 

 germ-cell is divided by a transverse septum 



* Unger, Botanische Beobachtungen, Entwick. 

 des Embryos von Hippuris vulgaris. Bot. Zeitung, 

 1849, p. 329. Sanderson, On the Embryogeny of 

 Hippuris vulgaris. Trans, of Bot. Soc. of Edinburgh, 

 Feb. 1850. 



Upper end of embryo-sac of the same as observed 



immediately before impregnation, 250 diam. 

 The tubular germ-cell, the lower end of which is 



embedded in the nucleated cells of the endosperm, 



occupies its axis. 



latter, which is the parent cell of the embryo, 

 is divided by a vertical septum into two 

 hemispheres. In these two new septa are 

 formed, also vertical, but at right angles to 



The same immediately after impregnation. 

 The germ-cell is now divided by a transverse sep- 

 tum into two compartments, the inferior of which 

 is the parent-cell of the embryo. 250 diam. 



the last. In the meantime, several new 

 vesioles make their appearance in the upper 

 tubular compartment of the germ-cell, which 

 eventually become cylindrical, and arrange 

 themselves, end to end, in its interior. The 

 four cells of the embryo now divide by hori- 

 zontal septa, which are succeeded by others 

 parallel to its surface, and meeting their pre- 

 decessors at angles of 45. The globular 

 body which is thus formed, consists of six- 



