HYPERTROPHIED LENTICELS ON THE ROOTS OF CONI- 

 FERS AND THEIR RELATION TO MOISTURE AND 

 AERATION 



By Glenn G. Hahn, Scientific Assistant, Carl Hartley, Pathologist, and Arthur 

 S. Rhoads, 1 Assistant in Forest Pathology, Investigations in Forest Pathology, 

 Bureau of Plant Industry, United States Department of Agriculture 



INTRODUCTION 



At the Bessey Nursery of the United States Forest Service at Halsey, 

 Nebr., warty excrescences were observed upon the roots of coniferous 

 seedling stock during the shipping season of 1915. Such excrescences 

 occurred on all pine species grown there. They were so abundant on 

 western yellow pine (Pinus ponderosa) 2 that the possibility of a parasite 

 as the causal agent was suggested, and the forest officers properly ques- 

 tioned the advisability of shipping the stock to other regions. 



Attempts were made by the writers to obtain evidence of a pathogenic 

 organism, but always with negative results. This experimentation con- 

 sisted of (a) incubation in moist chambers of portions of roots bearing 

 excrescences, (b) insertion of the interior portion of the excrescences, 

 removed with aseptic precautions, into nutrient agar, and (c) inocu- 

 lation of portions of the excrescences into roots of healthy 2-year-old 

 and 4-year-old Pinus ponderosa stock. 



After the failure to obtain evidence of a pathologic organism, a histo- 

 logical examination was made, which showed that the excrescences had 

 the structure of the hypertrophied lenticels (PI. 44) so commonly seen in 

 many dicotyledonous plants. 



DESCRIPTION 



The hypertrophied lenticles are found both upon the main tap root 

 (Pi. 45, B) and upon the lateral roots, not only close to the ground level 

 and upon the stems proper but also on the tap roots as far as 14 inches 

 (36 cm.) below the surface of the soil. 3 On the stems of conifers the 

 hypertrophied lenticles usually occur only on the basal portions of trees 

 growing in abnormally wet situations (PI. 45, A) or on parts otherwise 

 submerged. In exceptionally humid situations they may occur occa- 

 sionally on parts of the stems above the soil surface. 



1 The writers wish to acknowledge helpful suggestions from Dr. B. E. Livingston, of the Johns Hopkins 

 University, and Dr. T. H. Goodspeed, of the University of California. 



2 All the western yellow pine referred to in this paper was the type sometimes referred to as Pinus pon- 

 derosa var. scopulorum, from eastern Rocky Mountain seed. 



3 In all probability hypertrophied lenticels will be found at much greater soil depths on the roots of older 

 trees. 



Journal of Agricultural Research, Vol. XX, No. 4 



Washington, D. C. Nov. 15, 1920 



v i Key No. G-207 



(253) 



