﻿16 BULLETIN 24, U. S. DEPARTMENT OF AGRICULTURE. 



age, and continue to bear vigorously throughout most of their exist- 

 ence. The trees of the two sexes are usually unevenly distributed, and 

 female trees may sometimes be greatly outnumbered by males. The 

 seed matures, as a rule, during May or early June, when the capsules 

 open. 



The seeds are very minute, usually about an eighth of an inch long, 

 and sometimes no more than one-twelfth of an inch wide. They are 

 oblong, obovate, rounded at the apex, rather light brown in color, 

 and are surrounded at the large end with a fringe of long, white, 

 silky hairs which gives them a characteristic cottony appearance and 

 renders them extremely light and buoyant. Seed dissemination, 

 therefore, takes place easily, the seed often being carried by the wind 

 miles from the parent tree. Seed dispersion is also effected by the 

 overflow waters, which frequently leave fertile seed on the muddy 

 alluvial deposits far from the parent tree. 



The germinating power of freshly collected mature cottonwood 

 seed is comparatively high, varying from GO to 90 per cent. With 

 proper moisture conditions the seed germinates very quickly. The 

 vitality of the seeds, however, is very short-lived, few, if any, ger- 

 minating when more than a month old. Seeds three weeks old have 

 a germination of 50 per cent. 



Cottonwood is fastidious with regard to a suitable germinating 

 bed. Reproduction is almost entirely restricted to situations where 

 the mineral soil is exposed, and even on such sites the seed demands 

 abundant moisture. This explains why cottonwood seldom starts on 

 any situations except moist, newly formed sandbars or abandoned 

 cultivated fields. 



Reproduction by seed in the Mississippi bottom lands is probably 

 dependent to a considerable degree on the overflows which saturate 

 the surface soil. Even on areas not inundated the water table may 

 rise so near the surface as to supply the seed with sufficient moisture. 

 Reproduction seems to be surest on situations which have been inun- 

 dated, and every exceptionally high overflow is followed by a rank 

 growth of young cottonwoods wherever the shade and ground cover 

 will permit. It is probable that another benefit of this high water 

 lies in the thin silt deposit left by the receding water, which affords 

 an ideal germinating bed. 



FROM SPROUTS. 



Cottonwood reproduces also from sprouts, both from the stump 

 and from the roots. Root sprouts, however, are comparatively infre- 

 quent and from the standpoint of management are of minor conse- 

 quence. Stump sprouts originate both at the base of the stump and 

 the root collar, and at the top of the stump from the cambium be- 

 tween the bark and the wood. 



