3G0 TKAX8ACT10NS AND PKOCEEDINGS OF [Sess. lvi. 



food would interfere with the absorption of the latter, an 

 explanation which must be admitted from an evolutionary 

 standpoint. 



Following out the history of the young physiological 

 sporocyte or embryo-sac-cell, we find it at first of the same 

 size as the non-physiological sporocytes (iig. 7), but soon 

 greatly enlarged (fig. 10h,10 c, 10 d). This enlargement does 

 not, 2^c''' sc, produce compression and degeneration of the other 

 sporocytes, for one finds that the protoplasmic contents of 

 the latter retain their normal appearance for a considerable 

 time (figs. 8, 13 a). Later on, however, a marked change 

 takes place, due to "two causes, namely, starvation — as all 

 available nourishment is taken up by the embryo-sac-cell — 

 and pressure exerted by the surrounding nucellar cells. We 

 see, therefore, in fig. 11 the sister-cell >/ of the embryo-sac-cell 

 starved to such a degree that its lateral walls are no longer 

 able to resist the pressure of the surrounding cells, with the 

 result that they have been pushed in. Instead of the sister-cell 

 being the first to degenerate we frequently find the sporocyte 

 « of figs. 9^, 11, to collapse first as shown in fig. 14. 

 Soonei- or later all the other sporocytes are starved to death 

 by the euibryo-sac-cell, their nuclei and protoplasm travel 

 towards the apical part of each cell and there form a readily 

 stained mass (figs. 12, 13 «, x). Ultimately only traces of 

 the non-physiological sporocytes remain, forming a covering 

 for the apex of the physiological sporocyte, which Stras- 

 burger very appropriately calls the cap of the embryo-sac- 

 cell (figs. 15, X, y, 25-27, 29, 30). 



The physiological sporocyte or embryo-sac-cell at the 

 time of its formation is filled with finely granular protoplasm, 

 and possesses a comparatively large nucleus, poor in chro- 

 matin, and a nucleolus which occasionally seems to give rise 

 to a number of accessory nucleoli (fig. 8, E.S.). As the cell 

 gets older the chromatin-malter of the nucleus increases in 

 amount, the nucleolus swells markedly (figs. 9^ 11, 13 a, 

 13 h, 14),* and a vacuole makes its appearance close to 

 the apical part of the nucleus (fig. 12), increasing gradually 

 in size (fig. 15). The a])ical part of the embryo-sac-cell 

 seems to be the usual site in whicli the vacuole appears, if 



* The niinute structure of the nucleus and nucleolus will lie described later, 

 r. 383. 



