Germination of Forest Trees 



45 



According to that classification the most drought enduring are 

 Pinus divaricata, Pinus resinosa, Robinia pseudacacia, and Acer 

 rubrum. It is rather unusual to find Acer rubrum in this cate- 

 gory but the seed has such a thin seed coat that water absorption 

 is easier than in the case of a thick-coated seed. The intermediate 

 species are Pinns strobus, Pinus palustris, Abies balsamea, and 

 Catalpa speciosa (Neb.). Among what might be called the 

 moisture loving species are found Pinns taeda, Catalpa speciosa 

 (Ind.), Quercus rubra and Be tula papyrifera. 



On page 44 are given the germination curves of Pinus divari- 

 cata and Robinia pseudacacia. These sets of curves show that 

 as soil moisture decreases the beginning of germination is delayed, 

 the germination curve rises less rapidly and the final germination 

 per cent, is decreased. 



TABLE V 



The Effect of Soil Moisture on Germination 



Rocky Mountain Species 



Species 



OS 



t/5 



Dry Soil 



- - 



26 



34 

 22 

 12 

 14 



24 

 90 



48 



T3 en 

 o >> 



Oh" 



26 



6 



18 



6 



24 



. a 



:- u 



Pn 



26 



8 



39 



5 



9 



Medium Wet Soil 



0.5 

 5-0 



o-S 



a t/l 



12 

 22 

 20 

 12 

 12 

 80 

 20 

 18 

 18 

 20 

 14 



66 

 84 

 18 



.2 >> 



u rt 



36 

 18 

 16 



44 

 42 

 26 

 66 

 58 

 26 

 32 

 72 

 10 

 1 

 38 





48.0 

 17.0 

 6l.0 



54-o 

 60.5 

 12.0 



3-5 



6.0 



12.0 



6.5 

 21.0 

 3-0 

 1.0 

 9.0 



Wet Soil 



a 2? 



10 



14 

 14 

 12 



12 



24 



14 

 18 



14 

 18 

 36 

 36 

 30 

 24 



T3 cfi 



C >. 



32 



14 

 40 

 26 



42 



So 

 80 

 12 



34 

 30 

 52 

 36 

 30 

 50 



- a 

 a - ) 



58.O 

 52.0 

 56.O 

 63.0 

 91.0 

 38.O 

 22.O 

 10. o 



20.5 

 20.5 

 42.0 



4.0 



6.0 

 22.5 



As in the preceding table, Table V shows that the beginning 

 of germination is delayed in most cases and that the germination 

 period is considerably shortened with the decrease of soil moisture 

 content. Only 1 species, Pinus ponderosa (N. M.) showed a 

 higher germination per cent, in the medium wet soil than in the 

 wet soil, all other species show a higher per cent, in the wet soil. 



