532 MB. TT. MARSHALL WARD OX 



becomes directly converted into the embryo-sac, absorbing the 

 cells in the fore part of the nncellus as it does so. 



Emlyro-sac Sfc. in (Enothera biennis, (Plate XXII.) 



This is another ovule of which it is extremely difficult to get 

 sections sufficiently thin, and at the same time quite median. The 

 cells are remarkably small, and the growth very rapid, whence the 

 fact that the very young ovaries contain ovules far advanced com- 

 pared with other groups. But the difficulty becomes greater as 

 the ovaries get older ; for so brittle and hard are they from the 

 deposit of raphides that a razor's edge is turned at once : add 

 to these facts the abundance of granular material in the cells, 

 and reasons sufficient are given for obtaining very few good pre- 

 parations from a week's work. 



PI. XXII. fig. 1, shows how very early the one large embryo- 

 sac mother cell is established ; and sufficient has been said on the 

 subject to make intelligible the arrangement of the rows of cells 

 above and around this. The embryo-sac mother cell appears to be, 

 as before, an enlarged cell of the axial row ; and on tracing its fate 

 we find it (PI. XXII. fig. 4) cut by a diffluent wall into two equal 

 cells, each of which is again halved by a wall parallel to the first. 

 Whether the embryo-sac results from one or two of these cells I 

 cannot decide. 



J?mhyo-sac $c. of J^vethrumh&lstLminatum. (Pis. XXII -XXIV.) 



Having examined Senecio as the best-known Composite in this 

 connexion, the accounts given by Strasburger may be referred to 

 as embracing all the points satisfactorily *. But in Pyrethrum 

 and Antliemis there appears to be an abbreviation of the pro- 

 cesses we have hitherto observed. 



The cells are small, and the changes somewhat rapid. Pig. 1 

 gives a fair representation of the ovular papilla, seen in longitu- 

 dinal section at the base of the ovary of Pyrethrum. In PL XXII. 

 fig. 6, the embryo-sac mother cell is already conspicuous ; and a 

 comparison of the figures suggests that the nucellus arises by 

 the ongrowth of the apical portion only, u e. the part marked 

 oif by a line about the level of the base of this cell. In 

 PI. XXII. fig. 7, the sharp bend of the anatropous ovule is 

 established, as the single integument begins to arise. In the 



* ■ Die Angiosperm. u. d. Gyinnosp.' 1879. But cf. also Warming and 

 Vesque, loc. cit. 



