538 MR. II. MARSIIALL WARD OX 



cells ; for this depends on a general law of growth applicable to 

 all such organs as the ovule, anther, &c. Hence, while it is true 

 that the mother cells of pollen arise by the tangential division of 

 subepidermal cells in the anther, and the mother cell of the em- 

 bryo-sac also arises by division in the ovule similarly related to 

 the epidermis &c, it is equally true that other cells in the 

 ovule arise in the same way, and belong to groups of cells which, 

 from this point of view, are homologous with the axial group # . 



Nor can we hope to arrive at the nature of the embryo-sac and 

 its neighbours by such criteria as the nature of the cell-walls. As 

 Strasburger has pointed out, the diffluent cell-walls found in 

 pollen mother cells and the division of the embryo-sac mother 

 cell are equally due to the fact that they are soon to be absorbedf. 

 But probably the diffluent partitions in the embryo-sac mother 

 cell are also in part due to the producing cells approaching the 

 limit of division, and no longer having the power to form cellu- 

 lose envelopes, further division (the formation of the tetrahedral 

 groups of nuclei) being still weaker, so to speak, and no trace of 

 envelope appearing. If this be any argument, may we not 

 have in the separation of the two nuclei to opposite ends of 

 the sac a process differing in degree only from what has 

 already occurred in the formation of the " cap-cells " ? ; the occa- 

 sional appearance of a trace of cell-wall as cited above might lend 

 support to such a view. 



The above argument applies equally to the formation of the 

 tetrahedral groups of nuclei in the embryo-sac ; and, as Sachs has 

 shown, division in planes at right angles to one another is a com- 

 mon (perhaps universal) law of growth. Not only pollen-grains, 

 but embryos, trichomes, &c. show it. Hence, to arrive at any 

 conclusion as to the morphological nature of the embryo-sac and 

 contents, we are driven to other considerations than the modes 

 of division of the cell ; for the argument derived from this^leads to 

 ambiguity. 



The following is suggested. No one denies, probably, that in 

 the Angiospermous ovule we may expect to see the process of 

 reduction of the sexual generation (oophore) carried on somewhat 

 as in Grymnosperms, but to a further extent. This is not asking 

 too much ; for we find all the observers admitting it by the fact of 

 their attempting to explain the phenomena at all in terms applied 

 to vascular Cryptogams. 



And 



found 



