W. HOFMEISTER ON THE DEVELOPMENT OF ZOSTERA. 249 



membrane, transparent as glass, which encloses, as a sac, the 

 semi-fluid mass of primordial utricles set free by the solution of 

 the cell-coats (fig. 21). The large primordial cell in the centre of 

 this mucilaginous mass, the nascent embryo-sac, from this period 

 begins rapidly to displace the rest, which become by degrees 

 completely dissolved ; first of all those bounding it laterally, 

 while the cap of cells covering its summit persists for a short 

 time longer (fig. 21). The primary nucleus of the embryo-sac 

 is always still distinctly perceptible in its centre ; radiating 

 threads of granular mucilage pass out from it. Three newly- 

 formed, closely- crowded, globular cells show themselves in the 

 chalazal extremity, while at the micropyle end appear also the 

 now newly-formed nuclei of the germinal vesicles (fig. 21), as 

 three brighter, globular cavities, surrounded by dense granular 

 mucilage (the vesicles imbedded in. the protoplasm with more 

 transparent fluid contents). 



After the primordial utricle of the embryo-sac has also dis- 

 placed that hollow conical layer of dissolving cells which covers 

 its micropyle end, it becomes closely applied upon the now free 

 enveloping membrane*. This adhesion is so intimate at the 

 micropyle end, that in all subsequent stages the enveloping 

 membrane seems at this point to have been secreted by the 

 primordial utricle of the embryo-sac. Further down, from the 

 region where the cavity enclosed by the inner integument and 

 lined by the enveloping membrane (of the nucleus) becomes 

 widened and expanded into a cylindrical form, the growth of the 

 primordial utricle in breadth is frequently restricted; it then 

 runs on as a slender cylinder in the axis of the wider. The 

 tubular space between the enveloping membrane of the nucleus 

 and the elongated primordial utricle of the embryo-sac is filled 

 with finely granular mucilage coloured deep brown by iodine, 

 probably the product of the solution of the liquefied peripherical 

 cells of the nucleus (PL VII. fig. 23). 



These processes are accompanied by a very considerable elon- 

 gation of the embryo-sac and the enveloping membrane of the 

 nucleus, which both integuments follow by a rapid multiplica- 

 tion of their cells in the direction of the length of the ovule. 



* Formed by the persistent, connected outer walls of the superficial layer of 

 cells of the nucleus (see above). A. H. 



