NOV. is, 1920 Hypertrophied Lenticels on the Roots of Conifers 259 



CAUSES OF LENTICEL HYPERTROPHY 



Schenck (15) attributed lenticel growth on roots to oxygen hunger. 

 However, the association which has been observed between moist condi- 

 tions and abnormal lenticel growths, as well as experience in artifically 

 producing lenticel hypertrophy by placing cuttings in water or moist air, 

 have led more recent writers to suppose that for dicotyledonous plants 

 the hypertrophies are directly due to the presence of an unusual amount 

 of water (5; n, p. 72-80; 17). It is reasoned, in the first place, that 

 water or constantly moist atmosphere on the outside of the lenticels 

 allows the steady growth of the lenticels, while dry or intermittently dry 

 air tends to dry out the superficial cells of the lenticels or to increase their 

 solute concentration, with resultant chemical changes, including cork and 

 lignin formation. According to this idea the growth of the lenticel tissue 

 is controlled by transpiration through the lenticels; with intense trans- 

 piration the tissues become dried and the hypertrophy is checked. The 

 suberized or lignified layers thus formed are supposed to restrain mechan- 

 ically further proliferation on the part of the cells beneath them from 

 which the lenticel structures arise. So far this supposition seems logical, 

 though there is as yet no basis for a quantitative estimation of the im- 

 portance of tissue drying in the phenomenon. 



DeVaux has advanced another theory, based on the fact that the sup- 

 plying of abundant water to the absorbing surfaces and the reduction of 

 transpiration have both been found to be followed by lenticel hypertrophy 

 in experiments with dicotyledons. This writer supposes that both 

 these treatments result in increased sap pressure in the plant as a whole 

 and exert their influence entirely through increased sap pressure. He 

 does not apparently give sufficient weight to the possibility that both 

 decrease in transpiring surface and increase in soil moisture may involve 

 decreased oxygen supply as well as increased sap pressure. The limited 

 aeration of wet soils is a matter on which there is general agreement. 

 The necessity of soil oxygen for the normal development of mesophytic 

 plants, as indicated by common observation, has been recently confirmed 

 by direct experiments by Cannon and Free (j) and by Livingston and 

 Free (12). It is by no means certain that over- wet soil results in in- 

 creased sap pressure in mesophytic plants, especially since the last-named 

 authors find that a deficiency of oxygen in the soil results in some cases 

 in decreased water absorption. The association between swampy soil 

 and lenticel hypertrophy is at least as easily explained on the basis of 

 oxygen hunger as by DeVaux's " hyperhydrose " doctrine. 



The argument which Tubeuf (20, 21) seems to consider strongest 

 against oxygen hunger as the stimulus for lentical enlargement is the 

 fact that enlargement can be produced in cuttings in a moist chamber. 

 By placing cuttings with paraffined ends in moist chambers he secured 

 lenticel overgrowth, even in cases in which an atmosphere of oxygen was 



