June, 1931 



EVOLUTION 



Page eleven 



vides cotton so that the seed may be carried by the wind. Un- 

 fortunately this cotton is a handicap to growth and must be 

 removed before the seeds are planted. 



A large number of the hybrids were, of course, no more 

 vigorous than the parents, but fortunately many grew with 

 greater vigor than either parent. The trial was exceptionally 

 successful. About fourteen thousand seedlings were grown and 

 one hundred one new crosses were obtained. 



There is little to indicate in advance of actual trial which 

 crosses will yield offspring of noteworthy vigor. Rather more 

 than one hundred of the best-growing hybrids were reserved 

 and the remainder, nearly fourteen thousand, discarded. Each 

 of these better seedlings was propagated by cutting it up into 

 pieces ten or twelve inches long and stored for the winter. In 

 the spring they were planted in the field nursery and by the 

 next September each piece had become a six or seven foot tree. 



Quick growth, however, was not the only factor to be con- 

 sidered in the final choice of hybrids. The concern which is 

 going to invest in a reforestation project requires a good yield 

 per acre and wood of a quality that will suit both the lumber 

 man and the pulp manufacturer. Therefore, in selecting hybrids 

 for propagation from the hundred we chose the stocky trees as 

 against the slender ones of the same height, for the stocky 

 would produce the greatest yield per acre. The shape of the 

 tree was also important. A tree which is vertical and has few 

 branches is to be preferred over one that is crooked and has 

 heavy branches. Branches mean a distribution of the total 

 wood in the tree and many knots — a source of trouble to the 

 lumber man and pulp manufacturer alike. 



In order to determine the quality of the wood, fibre studies 

 were made and we found, as expected, that the length of the 

 fibre varied in different hybrids. As longer fibre gives better 

 paper and stronger lumber, we wanted to propagate the best 

 quality possible. We were much pleased to find that fibre 

 length and speed of growth were correlated. Thus, the fastest 

 growing hybrids were those with the longest fibre. 



Resistance to disease is also desirable and some of the hybrids 

 were tested for common forest tree diseases. The result showed 

 that many of the more vigorous hybrids were quite resistant 

 to the more common poplar diseases. 



The common wild poplars, P. tremuloides and P. grandi- 

 dentata, from which much of the book and magazine paper is 

 made, were compared with the hybrids. The studies disclosed 

 that the speed of growth, that is, the weight of wood produced, 

 of the new hybrids is from ten to fourteen times as much per 

 year as the wild poplars growing under similar conditions. 



After a tract of land is cut over it is customary to let the 

 saplings that remain grow to trees. Such natural reforesta- 

 tion, as it is called, yields about six cords of useful wood per 

 acre in sixty years, that is, an average of two hundred fifty 

 pounds of pulpwood, or one hundred twenty-five pounds of 

 cellulose, per acre-year. For cotton, the yield per acre-year is 

 one hundred and fifty pounds of cellulose, for flaxstraw — one 

 hundred pounds, and cornstalks, nearly five hundred pounds. 



Well managed reforestation plantations of pulpwood using 

 wild species will produce about two thousand pounds of cellu- 

 lose per acre-year. From the new hybrid poplar plantations 

 we have every reason to expect eighty cords of pulpwood per 

 acre in twelve years, that is, an average of about sixteen thou- 

 sand pouncb of merchantable wood per acre-year, equivalent 

 to eight thousand pounds of cellulose per acre-year. 



Cellulose Production Per Acre-Year 



Flaxstraw 100 lb. 



Cotton 150 lb. 



Cornstalks 500 lb. 



Reforestation — Natural 125 lb. 



Reforestation — Managed 2000 lb. 



Reforestation— New Hybrid Poplars 8000 lb. 



When trees can be grown so rapidly, they become an agri- 

 cultural crop, but without the uncertainties of annual plants. 



All calculations indicate that more dollars per acre-year of 

 wood can be grown than dollars per acre-year of wheat or other 

 common farm crops. But the whole value of reforestation is 

 not complete with the reckoning of the dollar value of the 

 wood grown. Such plantations protect the country from floods, 

 and from land erosion, and tend to preserve an even climate. 



Comparing width of annuLir rings, common poplar and mediocre 

 hybrid. (Reduced 1/3). Best hybrids show much greater width. 



