144 A PINE. 



It is important to observe also the long time required to 

 effect the development of the pollen-tube and the sub- 

 sequent fertilization, for about a year elapses between 

 the transfer of the microspore to the megasporangium 

 before fertilization actually occurs. More highly spe- 

 cialized plants, as some Angiosperms, grow pollen-tubes 

 many times as long as those of the pine in an almost 

 incredibly short time, often in the course of a few hours. 



The oospore germinates and produces the embryo 

 sporophyte. As this goes on, the whole sporangium 

 grows, and by the time the rudimentary root, stem, and 

 leaves are formed the outer parts of the ovule have become 

 dry and hard, forming the testa, and the embryo itself 

 has entered upon a dormant period. In this state the 

 whole structure constitutes a seed. 1 



As the ovule grows and ripens the upper surface of 

 the carpel becomes separated from the main body, and 

 remains attached to the seed as the wing. 



In the spring or early summer succeeding the ripening 

 of the seed, by the drying and warping of the carpels, 

 the cones open and the seeds are shaken out by winds 

 which, because of the buoyancy of the wings, carry away 

 the seeds to some distance from the parent tree. Under 

 favorable conditions the embryo resumes its growth, 

 emerges from the seed-coat, and begins to establish itself 

 as a new (pine-plant) individual. 



1 It will be interesting in this connection to review from ColeochceU 

 to Pinus the effect produced upon adjacent tissues by the act of fer- 

 tilization. See also " The Origin of Gymnosperms and the Seed Habit, " 

 by John M. Coulter, Bot. Gaz. 26 : 153-168, and "Origin of the Leafy 

 Sporophyte," by John M. Coulter, Bot, Gaz. 28 : 46-59. 



