352 



PLANT STUDIES 



are dry and powdery, and are scattered far and wide by the 

 wind. In the pines and their allies the pollen-grains are 

 winged (Fig. 309, i)), so that they are well organized for 

 wind distribution. This transfer of pollen is called pol- 

 Unationj and those plants that nse the wind as an agent of 

 transfer are said to be miemopJiilous^ or " wind-loving." 



The pollen must reach the ovule, and to insure this it 

 must fall like rain. To aid in catching the falling pollen 



the scale-like carpels of the cone 

 spread apart, the pollen -grains 

 slide down their sloping surfaces 

 and collect in a little drift at the 

 bottom of each carpel, where the 

 ovules are found (Fig. 310, J, ^). 

 The flaring lips of the micropyle 

 roll inward and outward as they 

 are dry or moist, and by this mo- 

 tion some of the pollen-grains are 

 caught and pressed down upon the 

 apex of the nucellus. 



In this position the pollen-tube 

 develops, crowds its way among 

 the cells of the nucellus, reaches 

 the wall of the embryo-sac, and 

 penetrating that, reaches the necks 

 of the archegonia. 



232. The embryo.— By the act of 

 fertilization, an oospore is formed 

 within the archegonium. As it is on the surface of its food 

 supply (the endosperm), it first develops a long cylindrical 

 process (suspensor), which penetrates the endosperm and 

 develops the embryo at its tip. In this way the embryo lies 

 imbedded in the midst of its food supply (Fig. 313). 



233. The seed. — While the embryo is developing, some 

 important changes are taking place in the ovule outside of 

 the endosperm. The most noteworthy is the change which 



Fig. 313. Embryos of pine : A, 

 very young embryos (ka) at the 

 tips of long and contorted sus- 

 pensors (s) ; B, older embryo, 

 showing attachment to suspen- 

 sor (s), the extensive root sheath 

 (wk), root tip (ws), stem tip 

 (v), and cotyledons (c).— After 

 Strasburger. 



