324 



THE NATURE BOOK 



an effect that is almost ungainly ; and 

 all the more so because of a tendency to 

 grow lop-sided, which is habitual tn these 

 trees. 



In spring they put forth early, long 

 before the leaves appear, a multitude of 



the intervention of fohage, these catkins, 

 growing out from lateral buds on the 

 previous year's shoots, are produced, 

 ripened, and their work accomplished 

 before the leaves begin to unfold. 

 The pollen-bearing catkins are long and 



Black Poplar. Aspen. 



LEAVES OF THE POPLARS, 



White Poplar. 



catkins, long and drooping, which often 

 completely clothe the trees. The Poplars, 

 amongst trees whose fruit-producing 

 flowers are fertilised by the wind's agency, 

 afford the best example of the most 

 a(l\-anced methods for its accomplish- 

 ment. They may be regarded as the 

 standard in this particular towards which 

 the other wind-fertilised trees are ap- 

 proaching. Cross-fertilisation, so essential 

 for the vigour of the race, is here assured 

 by the fact that the pollen-bearing and 

 the fruit-producing flowers are not only 

 grouped in separate catkins, but these 

 catkins are borne on separate trees ; 

 so that we have here pollen-bearing trees 

 and fruit-]M-oducing trees, separate and 

 distinct. In order that the pollen dust 

 may not be obstructed and wasted by 



pendulous, so loosely composed and hung" 

 that they shake out and scatter their 

 pollen dust with the slightest wind. 

 The fruit-producing catkins also, when 

 ready to receive the pollen, are pendulous, 

 quiver and shake, the more readily to 

 intercept it as it is borne past. As a 

 further precaution against failure the 

 pollen-bearing catkins are produced in 

 excessive numbers, so that the air becomes 

 crowded with the floating pollen grains. 

 Ha})hazard as would seem this method 

 of distribution by fitful agenc\- of wind 

 alone, failure of each tiny fruit -producing 

 flower to secure fertilisation is practically 

 impossible. When their work is done 

 the pollen-l)c'aring catkins fall and litter 

 the ground. 



In Slimmer, by the time the leaves are 



