LIFE HISTORIES OF FAMILIAR PLANTS 



floating in the atmosphere like a cloud of smoke. 

 After this comes a pause, and the little shelves once 

 more begin to accumulate their loads of pollen ; 

 the ends of the catkins go on lengthening out and 

 new scales are spread, and new stamens ripen. 



How beautifully adapted is the structure of the 

 catkin for the action of the wind ! The complex 

 arrangements of the insect-pollinated flowers are 

 marvellous indeed, but this mechanism for wind- 

 pollination is none the less wonderful in spite of its 

 simplicity. 



The pollen grains that float away so readily 

 are so small and light that they often travel for miles 

 even when borne by gentle winds. A microscopic 

 examination of the branches and bark of trees 

 during early spring will often reveal innumerable 

 pollen grains adhering to them on the sides that 

 have faced the wind, even when the trees are not 

 bearing catkins themselves and are growing at 

 some distance from those that do. This is especi- 

 ally noticeable when the wind arises after rain, 

 and the bark and branches are moist and therefore 

 retain the pollen grains. 



Indeed, pollen has sometimes been blown from 

 forests to distant towns and there accumulated 

 about puddles and over the surface of the ground, 

 where it has been mistaken for a fall of sulphur 

 and looked upon as a portent of coming evils, until 

 the botanist, by aid of his microscope, has re- 

 vealed its true nature. It follows, therefore, that 

 the grains of pollen must be exceedingly minute. 

 How minute they really are Fig. 35 (Plate 22) will 



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