NOV. 15. 1920 Hypertrophied Lenticels on the Roots of Conifers 261 



Nebr.) having a very sandy, well-drained soil, with a wilting coefficient 1 

 in the neighborhood of 3.4 per cent for the nursery as a whole, and an 

 unusually high proportion of the soil (79 per cent) in particles between 

 0.25 and 0.05 mm. in diameter. The results of a mechanical analysis of 

 this soil have already been published (8, p. 2). This, at first thought, 

 indicates sap pressure rather than deficient aeration as the cause of 

 hypertrophy. It is worthy of note, however, that in this case there was 

 frequent artificial watering in addition to considerable rainfall, and it is 

 therefore entirely possible that even in this case aeration was insufficient. 

 Buckingham (2} found that both diffusion and molar movement of gas 

 were slower in a wet sand than in any of the other soils, wet or dry, with 

 which he experimented. 



3. Reduction of the transpiring surface by removal of a large part of 

 the needles, or of the terminal growth, or both, resulted in distinctly 

 reducing the tendency to lenticel hypertrophy. (Table I.) The un- 

 pruned plants presumably had, at least part of the time, a lower general 

 sap pressure than the pruned. The result of the experiment therefore 

 tends to diminish the probability that there is any important causal 

 relation between general excessive sap pressure and the hypertrophy 

 in question. 



4. The rinding of the most abundant hypertrophy on roots which are 

 deficient in fibrous laterals or whose absorbing surface has been greatly 

 reduced by insect injury or by transplanting also tends to weaken the 

 hypothesis that excessive general sap pressure throughout the plant is 

 the chief cause of the hypertrophy. It is possible that roots which have 

 little absorbing surface will take less oxygen from the soil than would 

 better-developed root systems. An indication that this is the case is 

 seen in the experience of Livingston and Free (12, p. 185) with the oxygen 

 requirements of roots with different amounts of surface area. This 

 association between deficient root surface and lenticel hypertrophy may 

 therefore be an indication of a relation between oxygen deficiency and 

 lenticel production. 



The fact that lenticel hypertrophy was actually less in plants whose 

 leaf surfaces had been reduced by pruning not only tends to decrease 

 the probability of the ' ' hyperhydrose " explanation; it is suggested that 

 it is perhaps a further support for an oxygen-hunger (or carbon-dioxid 

 excess) hypothesis. Plants with their leaf surfaces reduced during the 

 latter part of the summer will of necessity produce less carbohydrate. 

 The smaller amount of carbohydrate reaching the roots in consequence 

 of the pruning might conceivably result in less respiration in the root 

 tissues and therefore in a decreased need for oxygen. If this were the 

 case the decreased oxygen hunger might furnish a partial explanation of 

 the slight lenticel growth in the pruned plants. 



1 Determined by the Office of Biophysical Investigations, Bureau of Plant Industry. 



