90 



of the membrane,, as is shovv^n more highly nagnified in fig. 

 95) 26. In the lower part of the cell, these are only narrow 

 meshes between the single thickened bands, Fhich also are 

 strongly developed.- in the upper part the bands are usually 

 flatter and sometimes partly interrupted* Thie case is a£. 

 special interest since, aside from the tyloses, it is the 

 only one knovm to me in which hypertrophic growth, incited 

 by wouiLd stimulus, is combined v;ith the formation of a 

 special kind of wall- thickening. Unfortunately I lacked 

 opporttinity for investigating a larger number of other or- 

 chids as to their callus-hypertrophies.l 



2 



Miehe has found in Trades cant ia virginica an object 

 of which the epidermal cells may easily be caused to form 

 callus-hypertrophy. If, by any kind of interference, cells 

 or cell groups of the epidermis are killed or destroyed, 

 the empty places thus produced are filled out by the living 

 neighboting cells. By growth, flat swellings are produced 

 on them, v^hich'grow into the dead cells. Ihe cavity is 

 finally closed, since all the neighboring cells hypertrophy 

 in the same way, and the cas formed from them lie close up- 

 (96) on one another. (Compare fig. 27). If a single cell closes 

 the wound, this h3^ertrophying cell can reproduce the nor- 

 mal appearance almost completely. Its growth reminds one 

 of the processes which were described above in the "resti-^ 

 tution of the tissue". Even the guard cells can share by 

 growth in the closing of the vvound. Vfliile normal cells are 

 perhaps 0.18 mm. long and 0.03 mm. broad, Miehe found hy- 

 pertrophying ones become from 0.38 to 0.43 mm. long and 0.08 

 mm. broad. Cell-division was not obser-^ed anywhere but it 

 may occur occasionally in Allium nutans , in which Hiehe ob- 

 served similar regeneration processes. 



Among callus-hypertrophies I include also the 

 abnormally large cells which Haberlandt^ recently 

 obtained in a culture of isolated tissue elements. 

 Isolated mesophyll cells from the upper leaves of 

 Laminum purpureum kept alive for weeks in Knop' s 

 nutrient solution or in nutrient fluids containing 

 sugar and gre# perceptibly at the same time thick- 

 ening their membranes either on all sides or only 

 .in places. Haberlandt*s statements concerning the 

 action of the chlorophyll grains are especially 

 interesting. In Knop's nutrient solution, they 



1. Ihe tendency of many orchids to the formation of reti- 

 culated membi-ane thicking, as proved by v. Bretfeld (see 

 above p. 61) , makes probable a positii^e issue for further 

 testing. It seems to have escaped v. Bretfield^s attention 

 that the formation of the described thickenings of the wall 

 can be combined with luxuriant hypertrophic growth. I sur- 

 mise that the occurrence of metaplasy or prosoplastic hyper- 

 trophy depends on external conditions. Cultivation in a noist 

 atmosphere might here, as so often, cai^se or favor the pro- 

 duction of abnormally large cells, iThrough lack of material, 

 I could not test this que^'tion further. 



E, Ueb.Wanderungen d. pfl, Zellkernes.Flora,1901,Bd. 

 LXSXVIII, p. 105. 



3, Eulturversuche mit isoliertin Pflanzenzellen Sitzungs- 

 ber. Akad. Wiss. Wien, 1902, Bd. CXI, Abt. I, p. 69. 



