260 Journal of Agricultural Research vol. xx, NO. 4 



provided. This seems at first glance to dispose of the oxygen-hunger 

 hypothesis quite effectively. However, an atmosphere of oxygen would 

 not necessarily insure an oxygen supply to the interior of a woody stem 

 unless the lenticels were already open at the time the cutting was placed 

 in the chamber. A section of stem removed from the plant and therefore 

 deprived of the oxygen that it would normally get from the leaves and 

 perhaps also from the roots, if its lenticels were closed, might easily by 

 oxidation of stored food materials develop abnormal partial pressures 

 of carbon dioxid in its interior tissues which would not be relieved till 

 the lenticels were opened by the stimulated growth which Tubeuf de- 

 scribes. The experience reported in his later paper, in which he records 

 interesting cases -of lenticel stimulation secured by covering bark with 

 impervious materials, and observation of lenticel hypertrophy on the 

 swelling above a heat lesion lead him to consider the stimulation 

 lenticel growth too complicated to be explained by any single factor so 

 simple as humidity. He still appears to consider oxygen hunger as 

 excluded from further consideration. However, his observation of 

 numerous lenticels on the stem of a heart-rotted spruce is the only refer- 

 ence that has been found concerning abnormal lenticel growth on any 

 part of a coniferous tree. 



The intumescences produced by Atkinson on tomato (i) and by Douglas 

 on potato (6) were clearly related in some way to excessive general sap 

 pressure. They are not analogous cases to the root lenticels here con- 

 sidered, since the hypertrophy in the intumescences was, so far as can 

 be judged from the illustrations given, mainly due to the stretching of 

 soft tissue cells already present rather than to the formation of large 

 masses of new cells. 



It may be of some interest to note in passing that Cowles (4, p. 553-554) 

 expresses himself as inclined to regard lacunar tissue in submerged parts 

 of water plants to be a response to lack of transpiration rather than 

 to oxygen deficiency. 



The present writers' findings bearing on the factors causing hypertro- 

 phy of subterranean lenticels on young conifers are as follows: 



1 . Hypertrophy is apparently limited to trees with their roots in water 

 or very wet soil. This may indicate either increased sap pressure or 

 decreased aeration as among the effective stimuli. It seems rather 

 improbable that there should be a significantly greater sap pressure in 

 a mesophyte like Pinus rigida or a semixerophyte like P. ponderosa 

 (Rocky Mountain type) in an excessively wet soil than in a plant in more 

 normal condition. This seems especially improbable in view of the slow 

 water absorption by the mesophytes in soil deficient in oxygen in the 

 experiments already referred to (12). 



2. While lenticel hypertrophy seems to be most common in soils con- 

 taining clay, it has been frequently found in one nursery (at Halsey, 



