166 



thinner until they showed a simple, weak, ring-like bast 

 circumv/illation, formed of lignified parenchyma". Toward the 

 top, the cords approached the central wood-body more and 

 more closely and were finally united with it. 



I 

 5?he conditions under which tuber-like gnarls are pro- 

 duced are not yet sufficiently understood. Sorauer states 

 that they are formed "readily near the outgrowing wounded 

 surface"; which argues in favor of the supposition that some 

 of the conditions created by the injury become the cause of 

 this forrar;tion, 



The isolated woody kernels of tissue which lie in the 

 bark of Fagus sllvatioa (fig, 72) and which have been thor- 

 oughly described by Krick as "bark ttibers", shov/ a still 

 greater diversity in development and histology, They are 

 either produced in connection with prevent it iocs buds or short 

 shoots which have been separated from the wood body of the 

 mother stem,- their cambium thi^s being descended ontogeneti- 

 oally from the normal cambium ring, in as much as it was con- 

 nected with it, at leaat at the beginning, or they are inde- 

 pendently formed of buds and short shoots without having any 

 connection with the mother stem. In the later esse, Kriok 

 distinguished between tubers with central wood bodies and those 

 which enclose cork tissue at their centre. The formation of 

 these bark tubers seems to havd nothing to do with any in- 

 jury and its results, 



Krick has collected the statements of earlier authors 

 ooneerning bark tissues (loc, cit). As one of the most im- 

 portant works may tee named here Tbhat by Gernet-*-. 



tl85) The gnarl-tubers of different Eucalyptus type s, al- 

 ready repeatedly studied, are of especial interest. They 

 ocGxir in the aaes of the first pairs of leaves and, ac- 

 cording to Jonsson^, are produced under the Influence of 

 unfavorable nutritive conditions. The dependence of 

 their growth upon that of the whole plant reminds,, one of 

 the correlation heteroplaamas mentioned above, Jonsson 

 could bring about the production of gnarl-tubers by cut- 

 ting off leaves, buds, or branches, 1, ©♦, he could nt^^^en.: 

 their growth. According to Vuillemin, the Eucalyptus 

 tubers are produced under the influence of a parasite, 

 Ustilago Vrieseana . which is said to cause tuber-like new 

 formations of other Myrtaceae (Myrtus, Acraena, Tristania, 

 Melaleuca, Callistemon)^»*. 



^ Ueb., d.Rindenknollen von Sorbus aucuparia. Moskau, 1860. 



^ Ytterligare bidrag till kannendomen om masurbildningar-' 

 na hos Myrtacerna, sUrskildt hos slflgtet Eucalyptus. Bot, Not., 

 1901, p. 181, further bibliographical citations there in. 



, 3 Vuillemin, S. 1. tumeurs ligneuses prod. p. une Ustilag- 

 inee Ohex.l. Eucalyptus. C. R. -^cad, Sc, Paris, 1894, T.CXVIIX, 

 p. 933, les broussins da Myrtacees, Ann, Sc, agron. Franc, et 

 etrang., T, II; compare Zeitschr. f. Pflanaenkrankh. 1896, Bd. 

 IV, p. 167/ 



* Further data on gnarl formation may be fouhd also in 

 Andreae: Abnorme Wurzelanschwellungen bei Allanthus glandulo sa. 

 1894, V. Kolb, Abnorme Wurzelschwell. bei CupresSus seperyir - 

 ene; Arcularius, Fall v. Wurzelkropf bei Abies Pichta , etc. 

 IM7 (Erlanger ]5iSsertations) , 



