GYMNOSPERMS: WHITE PINE. 



299 



considerably enlarged in fig. 340. The central axis of each 

 cone is a lateral branch, and belongs to the stem series. The 

 stem axis of the cone can be seen in fig. 341. It is completely 

 covered by stout, thick, scale-like outgrowths. These scales 

 are obovate in outline, and at the inner angle of the upper end 



Fig. 340. Fig. 341- Fig. 342- 



Staminate cone of white Section of staminate Two sporo- 

 pine, with bud scales re- cone, showing sporangia, phylls removed, 

 moved on one side. showing open- 



ing of sporangia. 



there are several rough, short spines. They are attached by 

 their inner lower angle, which forms a short stalk or petiole, 

 and continues through the inner face of the scale as a "mid- 

 rib." What corresponds to the lamina of the scale-like leaf 

 bulges out on each side below and makes the bulk of the scale. 

 These prominences on the under side are the sporangia (micro- 

 sporangia). There are thus two sporangia on a sporophyll 

 (microsporophyll). When the spores (microspores), which 

 here are usually called pollen grains, are mature each sporangium, 



or anther locule, splits down the middle as 



shown in fig. 342, and the spores are set free. 

 612. Microspores of the pine, or pollen 



grains. A mature pollen grain of the pine is 

 It is a queer-looking object, 



possessing on two sides an air sac, formed by the 

 upheaval of the outer coat of the spore at these two points. 



Fig- 343- 



Pollen grain of shown in fig. 343. 

 vhite pine. 



