256 W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTER A 



to assume a symmetrical form shortly before impregnation. The 

 micropyle becomes pushed downwards by active multiplication 

 of the cells on its outer side, turned away from the contiguous 

 angles of the four ovaries (fig. 42). A multiplication of the cells 

 of the opposite side of the nucleus commencing at the epoch of 

 impregnation, subsequently pushes the micropyle upwards again 

 with a great curvature of the entire ovule (fig. 43). The integu- 

 ments follow the increasing size and changing shape of the ovule by 

 multiplication of their cells in the directions of length and breadth. 

 After impregnation the process of multiplication and expansion 

 of the cells becomes very unequal, especially on the inner coat 

 of the ovule : much more active in the lower than in the upper 

 half, it pushes the endostome still farther upward (fig. 44), and 

 removes it from the endostome, which remains nearer its original 

 place, and consequently becomes diverted to the side. 



The impregnated germinal vesicle of Ruppia divides, as in 

 Zostera and Potamogeton, into a larger, upper, persistent cell and 

 a smaller, inferior cell which undergoes rapid multiplication. 

 During the gradual removal of the papilla (apex) of the nucleus 

 and of the endostome from the place of the germinal vesicle, the 

 pollen-tube, which remains outside the membrane of the embryo- 

 sac, extends itself, inside the place where it penetrates, through 

 the apex of the nucleus, by means of considerable longitudinal 

 growth of its tough membrane (fig. 43 b). 



The lower segment of the impregnated germinal vesicle very 

 soon becomes changed, by a series of longitudinal and transverse 

 divisions (figs. 43 b, 44 b), into a globular and subsequently an 

 ovate cellular body (fig. 45 b), from the side of which, below the 

 apex, shoots forth the first leaf-bearing axis. It unfolds its first 

 leaf close above its point of origin. After the imbedding of the 

 base of the leaf-bearing axis in the thick, fleshy, primary axis, 

 the first adventitious root grows out, in germination, opposite 

 the lamina of that first leaf (the cotyledon), forming a right angle 

 with the line of direction of the leaf. The margins of that lateral 

 face of the primary leafless axis which bears the leafy secondary 

 axis, rise up into a kind of -collar, enclosing the base of the 

 latter as a short, widely opened sheath (fig. 46). 



Irmisch*, in a clear explanation of the subsequent course of the 



* " On the Inflorescences of the German Potame<s," Flora 1851, p. 81 et seq. 



