7& 



on verymaiay other plants, presupposing that their bark is 

 exposed to the action of sufficiently moist air. At times, 

 in the case of the Ribes, the hyper trophied sigelling of the 

 "bark combines with abnormally increased growtti of v;ood, the 

 (83) cells of which in any case seem to be elongated radially. 

 A closer investigation of the different bark excrescences 

 might trell ioake known many histological details, worth con^- 

 sidering, although essentially the same symptoms are repeat- 

 ed;- elongation of the parenchyinatic elements of the bark, 

 chiefly in the direction of the radius, disappearance of 

 the cell-contents (starch, chlorophyll) and the omission 

 of every prosoplastic cell-change.-^ 



Sorauer has already treated the question as to the 

 external factors under whose action bark excrescences arise, 

 and has answered it experimentally^. According to him, the 

 causa morbi is excess of water. 



In my experimentation with Ribes aureum , I proceeded 

 as follows:- cuttings of shoots, several years old, were 

 put in a glass of water and also v/ere brought into moist air. 

 Even before the end of two weeks , the swellings described 

 and the first rifts are produced on the parts above the 

 water; after possibly four weeks, extensive excrescences 

 and gaping Wounds are visible;- under water, on the contrary, 

 the bark tissue remains normal. Potato tubers acted simil- 

 arly to the Ribes cuttings; on them too, the bark excres- 

 cenees were produced only in moist air, not under water. 

 In the case of Sambucus and Gingko, I frequently observed 

 vigorous swellings on the moistened part. Observations on 

 potato tubers proved at. the same time that even uninjured 

 organs can form bark excrescences. Since nothing is known 

 as to whether potato tubers form bark excrescences in moist 

 soil, Since further the excrescences are absent in tubers 

 lying in water, and since the immersed parts of Ribes cut- 

 tings retain their normal bark structure, it may be accepted 

 at least for these objects, that abundant supply of air is 

 one of the conditions causing bark hypertrophy. For its 

 production, as far Hke formation of the lenticel excres- 

 cences, the age 6f the tissue is apparently of no conse- 

 quence; at least, twigs of Ribes several years old as well 

 as young shoots (according to Sorauer) form fhe same bark 

 excrescences. 



The processes in Sambucus shoots and Ribes 

 cuttings described above in which even the young 

 periderm cells share in the hypertrophic change, 



1, Perhaps plants may still be found in which the cells 

 of the bark parenchyma are incited, under the influence of 

 water or moist air, not only to growth but also to division, 

 as (according to Devaux) the cells of many lenticels,- def- 

 inite nutritive conditions being taken for granted in the 

 plant under experiment. Schenck (loc. cit.), p. 568) ob- 

 served abundant division of the bark- parenchyma and the col- 

 lenchyma cells on the immersed parts of the stem of Artem- 

 isia vulgaris. It will be emphasized in the following sec- 

 tion also that division aften follows abnasflaal cell-growth 

 in other forms of hyperhydric tissues. 



8. Sorauer, Hand. 1. Pflanzenkrankh, p. 235, 236. 



