THE EMBIIYO-SAC IK ANGIOSPERMS. 533 



apex of the ovule are about three large cells, growing in length 

 as it grows. Each has a relatively large round nucleus, in which 

 are several bright spherical bodies in a granular matrix *, the 

 rest of the cell being filled with very coarse-grained protoplasm. 

 As the curving proceeds, and the voluminous integument creeps 

 over the nucellus, the latter grows in length (PL XXII. fio-s. 8 

 & 9) chiefly : it never becomes very large, compared with the 

 whole ovule ; and no transverse divisions occur in the three or four 

 cells which, side by side, fill up its interior. On the contrary, 

 these elongate, and are followed by the epidermis, until (PI. 



XXII. figs. 10 & 11, and PI. XXIII. figs. 1-6) the integument 

 meets at a point some distance beyond the apex of the nucellus, 

 leaving a large space, into which, as we shall see, the nucellus- 

 cells grow forwards at a later period. The epidermis of the 

 nucellus now ceases to grow, and soon takes on the peculiar bright 

 appearance of cells undergoing absorption. 



Indeed as early as PI. XXII. figs. 10 & 11 it is plain that one 

 of the large cells of the group in the nucellus has begun to develop 

 at the expense of its neighbours ; and a .careful comparison of 

 PI. XXII. figs. 10 & 11, and PI. XXIII. figs. HO shows that it 

 is not decided for some time which of the group is the fortunate 

 survivor. In PI. XXIII. figs. G-10, there are two cells apparently 

 about equally developed : they often appear to twist slightly ; and 

 to this cause I attribute the curious appearances seen in PI. 



XXIII. figs. 1, G, & 10. That this is really what takes place is 

 rendered more evident by transverse sections, which are easily 

 obtained by cutting across the capitulum. In PI. XXIII. fig. 1, 

 two cells have increased at the expense of(?) two others; and one 

 of these is apparently obtaining the mastery (PI. XXIII. figs. 



1-6). 



In PI. XXIII. fig. 5, a central large cell appears to have got 

 the upper hand of its two neighbours ; and even the epidermis- 

 cells have now become undistinguishable (PI. XXIII. figs. 7-10). 

 At a later period this cell (the embryo-sac) grows out, absorbing 

 the epidermal cells as it does so (PI. XXIII. figs. 11 & 12), until 

 the whole of the space in front is filled up, and the boundary fur- 

 nished by the integument supplies an apparent epidermis to the 

 sacf. The line across the lower third of the sac in fig. 12 



* Such nuclei are common in these Composite, and give the sections a pecu- 

 liar mottled appearance, 

 t Cf. Strasburger's account of Senecio, loc, cit. 



