120 



cause of the absence of the forest floor and of its work in the conservation 

 of moisture and the enrichment of the soil. 



4. It may be concluded that the most important factor in the growth 

 of trees is soil moisture. A confirmation of this may be found in the con- 

 ditions existing in areas of maximum development in number and size. 

 According to Sargent, the hardwoods of the United States find their maxi- 

 mum development in numbers and size in the lower stretches of the Wabash 

 Valley. In other words, in a region in which the soil possesses a rich water 

 content. 



In any forecasts as to the results of reforestation, or as to the rate of 

 tree growth in any given locality the supreme factor to be considered is the 

 constancy of the water content of the soil. 



5. In the case of the oaks an examination of the table will show a 

 period of rapid growth, a period of slower growth and finally a period of 

 scarcely appreciable increase. In the case of the walnut the growth is 

 much more uniform throughout the life of the tree. These are conditions 

 that would be expected if conclusion three is at all correct. 



6. It is probable that red and white oak in regions such as the one 

 studied have reached their full size at from eighty to a hundred years, after 

 which they begin to deteriorate. The few large forms introduced in the 

 table are from the lowest river terrace and were introduced for purposes of 

 comparison. 



7. The growth habit of the tr^e seems to control more largely than 

 external factors of growth. In a group of trees closely grouped the ma- 

 jority may show an exceptionally rapid growth in a given year, while one 

 or two show but a small increase. That this might be due to insect de- 

 foliation or other causes is of course possible, but an examination of the 

 growth through a series of years show a habit of slow growth as compared 

 with other individuals, whatever may be the external conditions. On the 

 other hand, individuals showing a habit of rapid growth are easily recog- 

 nized. No observable differences in the proportion of spring and summer 

 wood, in texture, in color or in any gross characters are to be observed in 

 these differing forms. Some individuals of each species are rapid growers 

 and some are slow growers, whatever may be the origin of the habit. It 

 was impossible to determirie whether or not this habit could be determined 

 by external features, as the trunks had been sent to the saw mill before 

 the area was found. 



8. The conditions of the area described are fairly typical and apply 



