1 88 



BOTANY. 



upper end there are several rough, short spines. They are 

 attached by their inner lower angle, which forms a short stalk 



Fig. i S 9. 

 Staminate cone of white 

 pine, with bud scales re- 

 moved on one side. 



Fig. 160, 

 Section of staminate 

 cone showing sporangia. 



Fig. 161. 

 Two sporo- 

 phylls removed, 

 showing open- 

 ing of sporangia. 



or petiole, and continues through the inner face of the scale as 

 a ' ' midrib. ' ' 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 sporo- 

 phyll (micro-sporophyll). 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. 161, and the spores are 

 set free. 



310. Microspores of the pine, or pollen 

 grains. — A mature pollen grain of the pine is 

 shown in fig. 162. 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. 

 When the pollen is mature, the moisture dries out of the scale 

 (or stamen, as it is often called here) while it ripens. When a 

 limb, bearing a cluster of male cones, is jarred by the hand, or 



Fig. 162. 

 Pollen grain 

 white pine. 



