THE EMBBTO-SAC IN ANGIOSPEItMS. 531 



cases this appears to result from laws of growth and cell-division, 

 and cannot be used as a test for determining homologies. 



Embryo-sac £(c. 0/*Lupinus venustus. (Plate XXI.) 



The practical difficulties of obtaining satisfactory preparations 

 of the embryo-sac in this genus (and even in Visum and other 

 Leguminosse) do not arise merely from the extraordinary number 

 of the small cells, but from their being crammed with granular 

 food-material from the earliest stages, and especially on account 

 of the oblique direction of the axis of the nucellus to that of the 

 carpel, whence longitudinal sections of the latter give oblique 

 sections of the former, in most cases. The main results of many 

 trials are given in the three figures. 



In PL XXI. fig. 1, obtained from buds when closely packed at 

 the top of the inflorescence, we find an axial row r , consisting of 

 one large cell below and three above, which have evidently been 

 cut off by transverse walls. The same process has also occurred 



in the other subepidermal groups of cells ; i.e. walls parallel to the 

 epidermis have cut them up into groups, which appear to radiate 

 from the lower part of the axial row to the periphery ; and on 

 comparing the figures with those given for Butomus, it is evident 

 that the same causes have produced the same effect, and that 

 here, again, an organ increasing in length, breadth, and circum- 

 ference does so by the cutting-off of cells by walls perpendicular 

 to the lines along which it is growing. 



In PL XXI. fig. 2, the same relations between the shape of the 

 organ and the arrangement of its cells is observed, and the lower 

 large cell of the axial row has become much longer, as has also 

 a lower cell of one of the lateral rows. If this figure be compared 

 with Strasburger's figures of Bosa livida*, no small resemblance 

 is noticeable ; and one ventures to suggest that, as in Butomus so 

 here, the arrangement of the cells depends on general laws of 

 growth, w r hence it follows that little argument as to the homo- 

 logies can be derived therefrom. 



PL XXI. fig. 3, shows just sufficient to demonstrate that the 

 cell-groups above and around the enlarging embryo-sac suffer the 

 same kind of deliquescence and absorption as do those in the fore 

 part of the nucellus in ffutomus. The exact details of the origin 

 of the embryo-sac from the large cell have not been followed; but 

 it appears probable that the large central cell in PL XXI. fig. 2, 



* 4 Die Angiospcrm. u. d. Gymnosp.' pi. iv. figs. 49-50. 



