140 



of the existing cells was incited by the injure (oaXlus-met- 

 aplasia); in others the cells laid baro showed an abnornBl 



frowth'and v;ere changed into voluainous vesicles and saos 

 callus -hyper trophy). In the preceding section A, it was 

 shown that even an increase of the normal tissue can result 

 from v/ound stimuli ( callus -homo opla s ia ) . 5?hoBe cells are most 

 (154) abundant in which after injury a heteroplastic tissue is pro- 

 duced by cell division ( callus -he ter opla s ia ) , 



In the majority of cases of callus hypertrophy (see above 

 p. 82) it v/as proved that the resulting large cells remained 

 below the normal cells of corresponding tissues in internal 

 formr.tion; the chlorophyll content being usually lost in hyper- 

 trophy. In rare cases the occurrence of ne^w characters TJas 

 associated with the abnormal growth (p, 95). 



Similar conditions exist In heteroplasias incited by in- 

 Jury. Excrescences arise, which are composed of cells of the 

 simplest form, very little differentiated, and are distinguish- 

 ed by this means from the ground tissue. They are all charac- 

 terized therefore as kataplasmas, 



Kataplasmas, produced after injury, differ very greatly " 

 among themselves. Either tissues resembling cork are produced, 

 termed wound-cork, or those similar to wood, called wound-wood, 

 or nearly homogeneous parenchyma masses which are composed 

 mostly of very thin v/alled, undifferentiated cells, often ab- 

 solutely irregularly connected. We term tissue of the last 

 kind simply callus. Also all plants and organs are not capable 

 of producing all three tissue forms after injury. 



We will begin our description with the homogeneous, par* 

 enchymatic "callus". 



We find representatives of very different plant groups 

 capable of forming callus tissue; algae and fungi often form 

 it, the vascular cryptogams less often. The c&llus tissue of 

 the phanerogams is of great significance; gymnosperms, monocoty- 

 ledons and dicot37'ledons , herbaceous and woody plants may form it 

 after Injury. We shall have to study especially thoroughly the 

 callus tissues of higher plants, 



First of all some examples may be given, from the list 

 of cryptogams . 



Algae . at least the larger tissue-formiJig marine sp®cies, 

 form t issue excrescences of simple histology, besides the well- 

 known adventitiotis shoots. The tiibercle-like callus in these^ 

 consists mostly of cells of one kind (ir of cambium and bark 

 layers with little evident difference. The cells are often 

 arranged in radial lines; at times they are somewhat larger than 

 the cells of the mother-foundation. Tubercles of this kind oc^ar 

 in Fuous, Polyides, Dellesseria, etc.-'- I found swellings in 

 Laminaria which grew out to the size of peas, possibly attrib- 

 utaaie to injury. X consider it very possible that the tuber- 

 cles, described by Sohmitz^, Vi/hich he traced to bacterial infec- 

 tion, have been produced by injury and cicatrization and that 



1 Kfister, Ueb. Vernarbungs -u, prolifikationserscheinungen 

 bei Meoresalgen. Flora, 1899, Bd. LXXXVI. p. 143. 



2 Ueb. knoll ohenartige Auswuchse an d. Sprossen einiger 

 Floriden. Bot, Ztg., 1892, Bd. L, p. 624. 



