2l8 



those of vigorous individuals ; on the other, by the lessened transpiration of 

 the bark because of greater humidity. Such conditions in the cherr}^ lead 

 to lenticel excrescences as is proved by experimentally producing an accum- 

 ulation of full cork in parts of the bark kept under water and further by 

 observing specimens naturally diseased. In this way it was discovered that 

 the cork excrescences preferred the youngest, well-leaved internodes in 

 which the bark formed folds. Such folds were produced, for example, in 

 places where the vascular bundles of the leaf left the axial cylinder and 

 pushed out the bark when passing into the petioles. 



Some other observations have been made showing that the decreased 

 evaporation due to increased moisture favors lenticel formation. Thus 

 vStapf^ in his studies on the potato, mentions that stomata develop into lenti- 

 cels if transpiration is arrested. Further, Haberlandt^ found that in the 

 horizontal branches of different trees (the linden, elm, honey locust, etc.) 

 the lenticels always occurred in greater numbers on the under side than on 

 the upper side, although counting the stomata on both sides gave approxi- 

 mately eciual numbers. The under side of the branch, inclined toward the 

 earth, will surely transpire less than the upper side, because of the greater 

 proximity of the soil and the lesser supply of air. 



The tan cushions in plum trees are essentially similar to those observed 

 in the cherry. As yet they have been observed only on old specimens with 

 diseased roots. I have known of only the initial stages in apricots. In all 

 varieties of stone fruits the cork excrescences were accompanied by marked 

 processes of bark loosening which in part resulted in the shoving of the 

 bast cords towards the outside. In young wood a weakly developed wood 

 ring and a reduction of hard bast bundles to isolated wide bast cells, filled 

 with a brownish-red gummy substance, was often noticed where the tan 

 disease had not broken out. Traces of gummosis were present everywhere, 

 and at times rich gum centres were found. In cherries, the especial sus- 

 ceptibility of certain varieties to. the tan disease may be recognized when 

 different varieties are planted close to one another, as, for example, in the 

 "black ox heart" and in "Winkler's white ox heart." 



All the cases which I have known originated on heavy soils or marshy 

 meadows. The history of some cases showed that the diseased trees had 

 been fertilized with stable manure or liquid manure. These statements in 

 connection with the anatomical conditions lead me to explain the tan dis- 

 ease as the result of an excessive water supply from the soil. When trees 

 are attacked during vigorous growth, they undergo such a disturbance that 

 the evaporation from the top is not sufficient to remove the excess of water. 

 The decreased leaf activity, or a partial loss of foliage due to atmospheric 

 influences or to pruning, should receive especial consideration. These cork 



1 Stapf, Beitrage zur Kenntnis des Einflusses geanderter Vegetationsbedingun- 

 gen etc. Verh. d. Zool-Bot. Ges. Wien; cit. Bot. Jahresb., VI. Jahrg., Section I, p. 214. 



2 Haberlandt, Beitrage zur Kenntnis der Lenticellen. Sitzungsber. d. Akad. 

 d. Wiss. in Wien, Vol. LXXII, Section I. July No. 1875. 



