88 



able ofetfter in;]ury to develop wouncL--fcissxie "by cell-division. 



We find callus-hypertrophies among thallophytes as well 

 as among higher plants. Only rarely does the histology of 

 the cells in this ahnormal grorrth remain similar to the orig- 

 inal normal one. Usually a' retrogressive formation of the 

 contents takes 'place. Here, as in the cells of the hyper- 

 hydric tissues, the degeneration of the chlorophyll apparatus 

 piays a large part, the cytoplasm too may often decrease 

 noticeahls?-. If progressive changes of the histological cell- 

 character appear during the hypertrophy, they involve only 

 the development of the membrane, llius among the cases be- 

 longing here, vje meet T3r,6sopI:aStio h ypertrophies alongside 

 of those which bear more or less distinctly the character- 

 istics of kataplastic hypertrophy. 



I obtained the most es:tensive callus^hyper trophies . on 

 thailo-ghytes in the case of Padina Pavonia . Little piecfes of 

 tlae broad ' thallus were cultivated for weeks in" sea-water con- 

 taining sugari the cells, laid bare by cutting, then grew out 

 into large, nearly colorless bladders, (compare fig. 24) which 

 always remained undivided; ThB walls of the hypertrophied 

 oells were very delicate. I observed further extensive callus- 

 hypettrophies on raggedly torn specimens of Uitophyllum tmoin - 

 »tum . the outer walls of the hypertrophied cells were greatly 

 thickened. Bitter observed cone-like thickenings of the walls 

 in callus-hypertrophies of Padina Pavonia .-*- 



In higher plants , at times in the tissues of the ases 

 (93) and leaves, it is easy to obtain callus-hypertrophies, and 

 they have often been observed^ Although in the algae above 

 named and in some 'others cell-growth alone is brought about 

 by Wound- St imulusj yet in my experience, in the case of high- 

 er plants, the cells of those tissues which can furnish callus- 

 hypertrophies are usually capable also of producing callus- 

 hyperplasias. External and internal factors ddetetmine whether 

 only undivided abnormally large cells are produced, or wound- 

 tissue with more or less ahundant cells. 



Axes 



Of the axillary tissues the bark and the wood-^parenchyma 

 show a Special "tendency" to the formation of callus-hyper- 

 trophies, 



' My observations were made mostly on cuttings of woody 

 plants, one end of which vi^as un^er water, the other extending 

 into moist air. The b ark cells' of many plants are often stim- 

 ulated under these conditions to hypertrophied growth. A few 

 examples should make clear the different kinds of changes ob- 

 served here. 



I observed regularly in cuttings of Cytisus that, near 

 the upper surface of the cut, the bark cells were enlarged 

 greatly and then grew about equally vigorously in all direc- 

 tions. Thus roughly ball-like or weakly lobated forms were 



1. Zur Anat. ua Phys. V. Padina Pavonia. Ber d. D. 

 Bot. Ges., 1899, Bd. JCVII , p. 2&5. 



