NOV. i s . 1920 Hypertrophied Lenticels on the Roots of Conifers 263 



RELATION BETWEEN LENTICEL HYPERTROPHY AND HEALTH OF 



PLANTS 



Sorauer (17, p. 210-219) nas used the name "tan disease" for lenticel 

 hypertrophy on roots and stems of fruit trees. His use of the term 

 "disease" appears justified in view of the association in many cases 

 between the lenticel hypertrophy and a general pathological condition of 

 the trees. The large lenticels described in the foregoing paragraphs as 

 occurring on conifers are undoubtedly abnormal and in that sense are 

 pathological. Since they occur only in abnormally wet situations, it is 

 to be expected that in many cases the pines on which they have been 

 found are unused to very moist surroundings and under the unfavorable 

 conditions are subnormal in general vigor. The hypertrophies were first 

 noted in a part of a nursery in which general vigor was unsatisfactory. 

 Comparisons of the less vigorous and more vigorous plants in the section 

 in which the hypertrophy was common showed lenticel hypertrophy 

 present in both the weaker and stronger plants. The first examina- 

 tion, made by Hartley on about 200 3-year-old transplants of Pinus 

 ponder osa, showed lenticel hypertrophy on a larger proportion of the weak 

 trees than of the stronger trees. Later examinations made by Hahn on 

 about 2,000 plants showed, particularly on P. ponder osa, that the greatest 

 number of hypertrophied lenticels were associated with vigorous growth, 

 This was true of plants in which the terminal root was rapidly advancing 

 and the roots were large and stocky but correspondingly undeveloped as 

 to lateral root surface. In one particular instance, however, where 2 -year- 

 old transplants of P. ponder osa had been badly affected by yellowing 

 due to excessive irrigation, 50 per cent of 95 vigorous plants examined 

 showed light occurrence of lenticel formation, while of no weakened and 

 dying plants 80 per cent were found to exhibit light occurrence, and 10 

 per cent showed pronounced occurrence. This same bed examined a 

 month later showed that the majority of the weak plants had died, while 

 the vigorous plants, or those beginning to show renewed terminal growth, 

 were alone showing freshly proliferating lenticels, those upon the dying 

 plants becoming darkened and sloughing off. It therefore appears that 

 lenticel hypertrophy is found on both weak and strong plants and that 

 the conditions which bring on their formation may, if sufficiently pro- 

 longed, eventually cause the weakening and death of the plant. There 

 is, however, so little direct connection between lenticel hypertrophy and 

 the pathology of the conifers that it seems logical to recommend that any 

 further investigation of the factors stimulating lenticel growth should be 

 made from the point of view of physiology rather than from that of 

 pathology. 



