250 W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTERA. 



The shape of the ovule becomes materially altered by this, passing 

 from an ovate form into that of a cylinder with a slightly at- 

 tenuated summit and a rather swollen base. 



The lower persistent part of the nucleus is now pear-shaped. 

 Its apex, as in Crocus and elsewhere, exhibits a funnel-shaped 

 excavation, lined by the chalazal end of the embryo-sac, in which 

 are confined the three " enigmatical antipodes of the germinal 

 vesicles* ^^ (fig. 23). The germinal vesicles themselves, now 

 fully developed, pear-shaped and large, with the inside of their 

 walls lined by a layer of protoplasm which encloses the now 

 lenticular nucleus, bear a similar relation to the micropyle end 

 of the embryo- sac (figs. 22-24). The primary nucleus of the 

 latter has by this time disappeared : if the embryo-sac has become 

 adherent at all points to the enveloping membrane of the nucleus, 

 secondary nuclei of a lenticular form are now frequently found 

 lying upon the inside of the wall of the former, and these are 

 mostly the centres of slightly developed systems of radiating 

 threads of granular mucilage (fig. 22). With the exclusion of 

 an exceptional case occasionally occurring in Z. minor, to be 

 mentioned hereafter, this is the only indication of a preparation 

 for the production of endosperm met with through the w^hole 

 existence of the ovule of Zostera. After fertilization these nuclei 

 disappear again, without having arrived even at a transitory 

 cell-formation. 



The ovule is now ready for fertilization ; during its develop- 

 ment the mouth of the rudimentary ovary becomes prolonged 

 into the canal of the style ; the filiform stigmas spring out later 

 through a more active multiplication of cells at two points of 

 the circumference of the orifice. The styles, which turn up- 

 wards at obtuse angles, are protruded at the period of flowering 

 from the slits of the leaf-sheath enclosing the inflorescence. 

 The anthers burst at the same epoch ; each half-anther opens 

 by a longitudinal slit running up over the septum dividing the 

 two loculi. The filiform pollen-cells arrive immediately upon 

 the arms of the stigma projecting into the burst half-anthers. 

 They are often found, singly or several together, spirally wound 

 round these arms. 



* A. Braun, Die Erscheinung der Verjungung, &c. Leipsic, 1849 (1851), 

 p. 297. 



