THE CARPELLATE CONE 371 



The carpellate cone. The carpellate cones have a complex 

 structure that cannot here be described in detail. They are 

 borne singly or in groups of two or three at the ends of the new 

 growth in tiie spring (Fig. 299, .4) simultaneously with the 

 staminate cones. Each cone is composed of scales arranged 

 somewhat spirally. Each scale (Fig. 299,7?) is believed to be 

 a group of three fused carpels (the point representing a sterile 

 carpel between two fertile ones). The scale bears a pair of 

 ovules below on the inner face, near the place where it is 

 attached to the axis of the cone. 



The ovule has a large nucellus, surrounded by an integu- 



O t/O 



ment, which bears two appendages looking like a pair of horns 

 in miniature (Fig. 299, B, o). The embryo sac which develops 

 in the center of the nucellus is one of a group of four cells, or 

 tetrad, which shows its relationship to a spore (megaspore) and 

 to the pollen grain. The other three cells of the tetrad fail to 

 develop, so that all the strength of the ovule is given to this 

 single functional megaspore which produces the female gameto- 

 phyte. The ovule is an outgrowth from the surface of the car- 

 pel, its nucellus (Fig. 300 A, n) corresponds to a megasporangium, 

 and the integuments (Fig. 300, A, i) are probably protective 

 investments. The integuments do not completely inclose 

 the nucellus, but there is left a small opening at the tip 

 (Fig. 300, J, //O called the micropyle. 



353. Pollination in the pine. The young carpellate cones are 

 upright when they first appear, and the scales are slightly sepa- 

 rated from one another. AVhen the pollen is shed in clouds 







from the stamens some of the grains are carried by the wind 

 to the carpellate cones and sift in between the scales, collecting 

 in little drifts near the ovules. This is the process of pollination. 

 At this time there are globules of moisture between the two horn- 

 like appendages of the ovules, and the pollen grains are caught 

 by these. The fluid gradually dries up, drawing the pollen grains 

 toward the micropyle, and finally into a cavity called the poll< n 

 chamber (Fig. 300, A. pc). which lies just above the nucellus. 



