288 Mr Carry, On the Development of [Nov. 27, 



inner segment in each lobe is in reality the primary-mother-cell 

 of the "pollen. Each primary-mother-cell, as seen in transverse 

 section, Avill be found when viewed longitudinally to correspond 

 to a. single longitudinal row of somewhat cubical cells rather 

 higher however than they are broad or long. Since only a single 

 row of primary-mother-cells is formed in each lobe the anther is 

 bilocular from the beginning and never at any period quadrilocular. 

 The outer or more superficial segment of the primitive archesporial 

 cell then becomes successively divided longitudinally in a tan- 

 gential plane in such a manner that in transverse section three 

 layers of cells are now apparent. In these latter radial, horizontal, 

 and further tangential divisions successively occur. The cells which 

 constitute the innermost of these three layers form by radial divi- 

 sion a peculiar epithelium of rectangular cells investing on the 

 inner aspect the primary-mother-cell : this is the tapetum. The 

 cells of the tapetum proper are reinforced by a corresponding layer 

 on the external side of the anther-lobe, formed by means of a 

 series of internal segments cut off vertically from the cells of the 

 parenchymatous ground tissue in that region. In this manner a 

 limiting membrane is formed which entirely surrounds and invests 

 on all sides the primary -mother-cell of the pollen. 



The tapetal cells proper are thus derived from a portion of the 

 primitive archesporium, while those cells by which the layer is 

 completed towards the outer side of the anther, and which appear 

 in transverse section to be longer and more oblong than the real 

 tapetal cells, are not so derived. Each cell of the limiting mem- 

 brane contains a prominent nucleus surrounded by granular 

 protoplasm. 



The primary-mother-cell of the pollen is when viewed in 

 transverse section at first somewhat hexagonal in shape, single 

 and of relatively large size, for while the outer segment of the 

 archesporial cell has continued to undergo division, no further 

 division has taken place in the inner segment which has very 

 granular protoplasmic contents and a distinct nucleus. 



Very soon however it may be found exhibiting two nuclei pro- 

 duced by the division of the single one, and this nuclear division is 

 speedily followed by division of the protoplasm into two portions, 

 and formation of a longitudinal septum in a direction somewhat 

 oblique to the surface of the anther. Each of these two cells now 

 begins distinctly to elongate in a direction perpendicular to the 

 surface of the anther, and by virtue of this elongation they become 

 very sharply differentiated from the surrounding tissue. As the 

 loculus expands by growth of its walls, this elongation becomes more 

 and more pronounced. Immediately after this change has become 

 fairly well marked, each of the two cells becomes divided by longi- 

 tudinal division parallel to its long axis, and this is followed by a 



