GRAINS OF PINE POLLEN 
They show little tendency to stick together, whereas the pollen of plants 
that depend on insect visitors is often exceedingly sticky, so that it 
will adhere to the legs and bodies of insects. The pollen of the pine is 
much smaller than that of most plants; it is here shown as seen by 
reflected light. Photo-micrograph by David Fairchild. (Fig. 9.) 
THREE-CELLED POLLEN GRAIN 
The pollen of pines is adapted to travel with the wind 
by the possession of wing-cells or balloons. The 
grain consists of three cells, one of which is fully 
developed and contains the nucleus, while two at 
the sides are hollow and contain nothing but air. 
They buoy up the nuclear cell and enable it to 
travel almost incredible distances—as far as 400 
miles in extreme cases. Drawn by W. H. Lamb, 
of the U.S. Forest Service. (Fig. 10.) 
