84 MR. Т.Н. CORRY ON THE POLLINIUM OF ASCLEPIAS CORNUTI. 
Fig. 6. A stage still later. The mother cells, mc, of the last stage have each divided longitudinally into 
two in a plane at right angles to their length, so that they now form two rows; the other parts 
are lettered as before ; con, the connective tissue. 
7. Still more advanced. Each mother cell has again divided longitudinally into two in a plane at 
right angles to its length, so that from each mother cell a row of four cubical cells has been 
derived ; these are the special mother cells of the pollen, smc. The other parts are denoted 
by the same lettering as in the previous figures. 
8. Portion of an anther seen in transverse section at a later period, the parts named as in the last 
figure. The special mother cells have now become rounded, but are still connected with one 
another. Considerable changes have taken place in the cells immediately external to those, 
tap, tap*, which form together the limiting tapetal membrane; the walls of the former are 
much compressed, and the cell-cavity in some cases is almost obliterated. 
9. The same at a more advanced stage still. The tapetal cells, Фар“, have become divided to form two 
layers ; the wall of each of the tapetal cells, tap, tap*, which is adjacent to the special mother 
cells has become in part cuticularized ; and this transformed portion forms a continuous sheet 
of a pale yellow colour, p w, enclosing the whole of the special mother cells, s m с, the cell-walls 
of which are still unchanged. This sheet forms the external coat of the pollinium; 1, com- 
pressed remnants of the rows of cells external to the tapetal membrane in earlier stages; g, the 
row of cells originally internal to the single row of tapetal cells proper which has persisted. 
10. Transverse section of a nearly adult pollinium removed from the anther-loculus: ри, external 
cutin coat of the pollinium ; sm c, special mother cells, now become polyhedral, whose walls, 
sm w, have likewise become cuticularized. 
11. Fully adult pollinium, seen in transverse section. The contents of each of the special mother 
cells have contracted slightly from Из cutin wall, and formed over the whole surface a thin, 
delicate, cellulose membrane, in (“intine ”), thus becoming converted into a pollen-grain. Тһе 
section has been treated with absolute alcohol, so that the contents have contracted away 
from the newly formed wall, i», which is then rendered evident by staining with methyline blue. 
Several of the pollen-grains are seen exhibiting two nuclei. 
