THE PROMISE OF THE PLANT THAT IS TO BE 497 



FIG. 630. HOP HORNBEAM (Ostrya carpinifolia). 



Female catkin, and one involucre opened to show the seed. 



through the air. It is 

 impossible to open a 

 pine-cone before its 

 time without hacking 

 it to pieces, and yet 

 the mechanism by 

 which the opening is 

 effected naturally is 

 very simple. The cen- 

 tral column or stalk 

 to which the scales 

 are attached begins to 

 grow, and this has the 

 effect of separating all 

 the scales. The wing 



^ Vjf wtyyuu t, t & 



indica). of the seed is an upper layer of the scale, from which it 



Bidged seed. becomes detached when the seed is ripe. In a breeze sufficiently 



strong to pick them from between the scales of the cone, the 



seeds go spinning through the air to a distance of eighty or a hundred 



yards. In the Hop Hornbeam (Ostrya carpinifolia) the seeds are contained 



in inflated involucres, which hang in catkin-like clusters from the branch, 



and are readily borne about by the wind (fig. 630). In the Hornbeam 



(Carpinus betulus) the involucre is very large and three-lobed. In the 



Birch (Betula alba) the seeds, to a great number, are borne in cylindrical cones, 



the scales of which loosen in dry weather to set them free. They are quite 



small, but each is provided with a pair of thin wings, upon which they flutter 



away from the tree like a swarm of tiny flies which indeed they closely 



resemble. So abundant is this seed-fall that where birch trees are plentiful 



the ground around them appears to be covered with a thick coating of bran. 



The seeds of the Willow-herb (Epilobium') and some other plants are 



FIG. 631. YEW (Taxus baccata). 



Fruiting shoot showing development of the arillus. (a) Female flower surrounded by scale-like bracts. (6) A later ?tage : 

 the arillus (r) growing up around the seed, (c) A ripe seed surrounded by the fleshy red arillus. 



n14 



