January, 1922 GROWTH OF TREE SEEDLINGS AND WHEAT 69 



On June 12 all flats received a row of marquis wHeat kindly furnished by 

 H. L. Shantz, of the Bureau of Plant Industry. The mild lime series was 

 sown with the same species on June 23, except wheat, which was put in on 

 June 24. 



All flats were protected from birds and rodents by rust-proof wire netting 

 with a 6 to 7 mm. (about quarter inch) mesh, since it had been found in 

 previous work of this character that coniferous seed in unprotected flats is 

 largely destroyed. Perhaps the flats attract curiosity and expose the seed to 

 more danger than in a forest nursery. The wire cut off a certain amount 

 of sunlight, perhaps about 20 percent or more ; this was an advantage, since 

 exposure to full sunlight is not beneficial to very young coniferous seedlings. 



Measurements of the- growth in height were made at about five-day inter- 

 vals up to August 4, and then on September 12. The measurements were 

 taken from the ground to the base of the cotyledons, and when the primary 

 leaves appeared these were measured and their length added. The growth 

 of the maple was taken by measuring the length of the primary leaves alone. 



At the end of the season the growth of the roots for the entire period 

 and the green weight of the seedlings were determined. 



Results 



The results on the unlimed, strong lime, and mild lime series will be 

 presented separately. The first series shows the influence of humus, and 

 the second and third the influence of alkalinity and of lime in different pro- 

 portions. The rate of growth is shown in the accompanying curves, figures 

 I, 2, 5, and 6, and the data on root growth and green weight is presented 

 diagrammatically in figures 3 and 4. 



Influence of Humus 



Rate of Growth in Height. — The rate of growth in height of each species 

 has been plotted separately, but all three soils in the series are placed for 

 comparison on the same graph. The results of the mild lime series have been 

 included in the humus graphs for pitch pine, jack pine, and red pine, figures 

 I and 2. 



The differences shown are in no wise due to the effect of humus upon 

 water relations, but upon the nutrient properties of the soil — its fertility. 

 The physical properties of the soil do not enter into the problem except 

 through effect on aeration, and in this series all the soils were porous enough 

 to give abundant oxygen to the roots. 



The favorable influence of humus shows strikingly. In spite of acidity 

 there was far more rapid growth of all species on pure humus than on pure 

 sand (see figures i and 2). The cause is almost certainly the nitrogen con- 

 tent of the humus and the lack of it in the sand. The nutrient value of 



