in.l CONIFERS. 2<)7 



to do with the mode of transference of the pollen from 

 the male flowers to the ovules, which is due to the wind. 

 Dense clouds of the pollen are carried in the air often to 

 a considerable distance, giving rise sometimes to so-called 

 "showers of sulphur." When the pollen finds its way to 

 the apex of the ovule the extine, or outer coat of the grain, 

 shrivels up and separates from the intine. At about the 

 same time a portion of the protoplasmic contents of the 

 grain accumulates at about the middle of its broadly- 

 rounded back and becomes separated from the rest by 

 the formation of a cell-wall, convex towards the cavity of 

 the parent-cell. The new cell is much the smaller of the 

 two and undergoes no further change (in Pine), while the 

 intine of the larger one grows out directly into the pollen- 

 tube, the complete elongation of which is not attained until 

 about a year after the shedding of the pollen in those Firs 

 in which the fruit is of biennial maturation. 



In Pine the embryo-sac originates in the axis of the 

 ovule as in Angiosperms, but it is usually imbedded rather 

 deeply in its substance. It becomes early filled, long pre- 

 vious to contact of the pollen-tube, with cellular tissue 

 (an endosperm) originating by free-cell formation like the 

 endosperm of Angiosperms. Certain of these cells in the 

 embryo-sac near its upper boundary enlarge as secondary 

 embryo-sacs (formerly called corpuscida and by some now 

 called ai'chegonia, upon the assumption of their homology 

 with the so-called organs of vascular cryptograms), 

 within each of which, upon contact of the pollen-tube, 

 the formation of several embryos is determined by 

 the repeated division, in the direction of the axis of the 

 ovule, of a cell at the base of the cavity of the secondary 

 embryo-sac. Upon the number of longitudinal divi- 

 sions of this cell (first stage of the pro-efnbryo) depends 



