46 MARGARET C. FERGUSON 



ment has closed over the pollen-grains and the macrospore 

 mother-cell has divided giving rise to an axial row of cells the 

 lowest of which becomes the functional macrospore (fig. 69, 

 plate VI). 



The Pollen- chamber. The pollen-grains fall upon a scale 

 and slip down to its base where they come into contact with the 

 extended arms of the ovule. These prolongations of the integu- 

 ment now straighten and partially draw together thus bringing 

 the pollen-grains down into the wide micropylar canal (fig. 

 123, plate XII, and fig. 66, plate VI). The free limb of the 

 integument is seen in section to consist, at this time, of three 

 layers of cells. As soon as the pollen-grains have found their 

 way into the lower portion of the micropylar canal and some, 

 at least, have come into contact with the tip of the nucellus, 

 the cells constituting the middle layer of the arms, at a point 

 slightly above the apex of the nucellus, elongate rapidly. The 

 bulge or protuberance thus formed extends inwards from all 

 sides and meets, closing the opening above the pollen-grains 

 (figs. 66 and 67). As soon as the opening has been closed 

 and the pollen-grains secured, these elongated cells give 

 rise by division to many smaller ones (fig. 68). By the rapid 

 elongation of these cells the safety of the pollen-grains is as- 

 sured in a very short time, and then cell multiplication follows 

 leisurely. This very pretty mechanism by which the final clos- 

 ing of the micropyle is effected has not been previously described 

 for any Gymnosperm, unless it be noted in Shaw's ('96) state- 

 ment, unaccompanied by figures, that the micropyle in Sequoia 

 is closed by the radial elongation of the cells about it. 



The depression in the apex of the nucellus in the Abielinea 

 at the time of pollination, described by Hofmeister in 1851, and 

 since noted by many writers, has, it seems to me, been greatly 

 exaggerated so far as Pinus is concerned. The expression 

 " cup-like depression " is not infrequent in literature, but, in so 

 far as my observations go, saucer-like is as strong a term as one 

 is justified in using (figs. 66, 67 and 69, plate VI, and 75, plate 

 VII). At the time of pollination the upper concave portion of 

 the nucellus terminates in a row of more or less elongated 

 cells, which are not closely united at their free extremities, but 



