32 Richard H. Bocrker 



Soil temperature was not measured. With the air temperature 

 at an optimum point during the entire experiment it is reasonable 

 to assume that the soil temperatures were likewise always at an 

 optimum, at least they were never at such a low nor at such a 

 high point so as to affect materially the germination of the seeds 

 or the growth of the seedlings. 



Notes on Damping-Off 



No special investigations were conducted to determine what 

 species were most affected and what conditions of light, moisture, 

 and soil were most favorable for the development of this group 

 of fungous diseases. This part of nursery practice is a problem 

 of no small importance in itself and the only data here given is 

 that which had to be taken in connection with this series of in- 

 vestigations. Therefore these are merely notes and suggestions, 

 which, while conclusive as far as they go, must be substantiated 

 in the future to be of any permanent value. 



It was found that the pines were most affected. Pinus divari- 

 cata at the end of five weeks was affected most. About 15 sepa- 

 rate cultures of 200 seeds each of this species were started and 

 most of these showed more or less serious effects of the disease. 

 Several cultures of Pinus resinosa failed after six weeks. Pinus 

 palustris damps off in loam before it really gets its crown above 

 ground. In this case the loss was reduced in the sand and gravel 

 cultures. Both the New Mexico and South Dakota varieties of 

 Pinus ponderosa after five weeks damped off considerably, leaving 

 only from 1025 P er cent, of the original stand. The following 

 is a list of species in the order in which they were affected in 

 loam under normal conditions of light and water. The first men- 

 tioned were affected most : 



Pinus divaricata Pinus ponderosa (N. M.) 



Pinus resinosa Robinia pseudacacia 



Pinus palustris Pinus strobus 



Pinus ponderosa (S. D.) Pinus taeda 



It appears that the seeds of trees of certain habitats when 

 germinated in soils or under conditions different from those ob- 

 taining in their natural environment are affected worst. These 

 habitats are : 



