Germination of Forest Trees 87 



height growth in the loam and the least in the gravel. Compar- 

 ing this conclusion with No. 10 it is interesting to see that the 

 conifers do well in either sand, loam or gravel, but that the hard- 

 woods do best in loam only. 



12. Pinus ponderosa, and Quercns rubra show the greatest 

 length of tap root and greatest length of lateral roots in the gravel 

 and the shortest length in the loam ; Robinia pseudacacia shows 

 the greatest length of tap root in the sand and least in the loam. 

 In other words, root development is usually greatest in the gravel, 

 and least in the loam. This conclusion agrees in part with 

 Tolsky's results that pine in black soils develop vertical roots but 

 in sand develop a greater spread of lateral roots. 



13. As far as height growth goes it is evident that pines, on 

 account of their greater drought resistance, may grow as well in 

 sand or gravel, or even attain a greater height in sand or gravel 

 than in loam ; while hardwoods which prefer moister soils grow 

 best in loam. That root development is greatest in gravel is due 

 undoubtedly to the fact that water quickly percolates through this 

 soil and hence the roots have to go deep for the moisture. 

 Reference to the diagram on page 85 will bring out these rela- 

 tions more clearly. 



III. The Relation of Size and Weight of Seed to Germination 



and Early Development. 



1. Large seeds of Pinus ponderosa and Pseudotsuga taxifolia 

 produce a higher final germination per cent, than small seeds. 

 This conclusion contradicts the results of Busse and Centgraf 

 who found no relation between size of seeds and germination per 

 cent., but it proves the contentions of many old silviculturists 

 that large seeds produce a higher germination per cent. 



2. At the age of from 2 to 4 days large seeds of Pinus pon- 

 derosa and Pseudotsuga taxifolia produce larger seedlings than 

 small seeds. This conclusion proves at least in part Schlich's 

 statement on page J3 concerning the use of large seeds in plant- 

 ing and nursery work and bears out the contentions of practicing 

 foresters in Europe that large seeds should be used in field 

 sowing. This conclusion likewise agrees with the mass of evi- 

 dence collected in connection with many cereal and garden vege- 



