156 PRACTICAL BOTANY. 



illustrate various stages of development (i.e., at short intervals 

 during May and June). By cutting sections from such material, 

 and treating as above directed, the history of development of the 

 pollen may be made out. 



D. Mount ripe pollen-grains (i.e. such as may be 

 collected by shaking a male branch in June) in dilute 

 glycerine, having previously wetted them with alcohol. 

 Observe 



1. The two large lateral Wings, usually filled with 

 air, which facilitate the carriage of the pollen by the 

 wind. These are extensions of the outer coat (extine). 



2. The central body of the pollen-grain consisting 

 of 



(a.) A large cell, which constitutes the greater part 

 of the grain, and from which the pollen-tube springs. 



(b.) A series of one or more smaller vegetative cells, 

 affixed laterally to the wall of the pollen-grain at a 

 point between the wings. These take no direct part 

 in the formation of the pollen-tube. 



II. Female branches or Cones. Observe on a 

 Scotch Fir, towards the end of June, that there are cones 

 to be found in three different stages of development, the 

 position of which is constant. 



(a.) Small green cones occurring (one or more) close 

 to the apex of the shoot of the current year. Note that 

 the basal part, or stalk, bears brown membranous scales, 

 while the upper part is globular, and is marked out 

 into numerous square areas, which are the apices of so 

 many Ovuliferous scales. 



Comparing a shoot, which bears such young cones, with an 

 ordinary vegetative shoot, it will be seen that the cones correspond 

 in position to the lateral buds, of which they are the morpho- 

 logical equivalent. 



