X62 



velops oallus. 1 know of only a fsw cases in which callus is 

 formed s|.raultan6oxisly on the end under water. A very small 

 "vTater-oallTis" is produced in cuttings of populus pyraroidalls . 

 in tJift formation of which, in my experience^ only the oamTbiuni 

 participates v-^hile bark and pith retoain inaotJ,tre, I fmind 

 oallus produced in Samhucua and Ligustrum under water by the 

 activity of the bark tissue, when the conditions were similar. 



If, in the last named case, the cut surface fails to form 

 oallus in sand, the arrested respiration and transpiration may 

 indeed be to blam© for it. However, callus may be formed in 

 the end in the sand, if the action of-the dry air makes its 

 forEation impossible at the other end"*", That portion is there- 

 fore preferred for this formation which is at the time undOr 

 most favorable conditions. 



Also, if the foraatipn of oallus tn cuttings is temporar- 

 ily arrested by unfavorable conditions^ the tissue does not on 

 'this account lose the ability to form it. I found oallus tis- 

 sue produced to the usual amount on poplar cuttings, which had 

 lain about four weeks under water, after they had been brought 

 into a moist room. Titmann obtained the same result. He put 

 the cut surface in plaster oasts and then, after removal of the 

 plaster bandage, found them developing callus. Titmann calls 

 attention further to the fact that poplar cuttings, with scars' 

 left on the main axis by the falling off of dead side branches, 

 form callus on these already healed wound -surfaces through the 

 action of a moist atmosphere. "Therefore the scarred wound 

 acted in this just as a fresh, unscarred one would have done. 

 The results of the injury therefore allow a contimxance of con- 

 ditions, which later make possible the formation of the oallus". 



Correlations exist further between the formp-tion of callus 

 tissue and the development of side shoots. on the cuttings. Ho 

 case is known to me, in which the production of a callus would 

 have been completely suppressed as the result of an abundant 

 . formation of side shoots (favorable conditions being presup- 

 posed), but indeed its development is often retarded to the ben- 

 efit of the side shoots. 



In conclusion, still a few words concerning "pofjarity". 

 An object suitable for the study of this is again offered by 

 the oftnamed poplar cuttings. Even under equal external condi- 

 tions, the capacity of both cut ends for forming callus is not 

 perfectly equal. If a nuj|ber of cxxttings are placed in water, 

 some upright, some inverted, with the upper out surfaces favor- 

 ably arranged for callus formation, it is found that the in- 

 verted examples develop a more luxuriant callus than do those 

 normally oriented: the basal poles are capable of a more abun- 

 dant formp-tion of oalHus tWn the apical. 1 observed the some 

 phenomenon in Rosa* Fvf^m the observations of other authors, 

 on girdled stems and the like, it takes place also in a number 



1 Compare also Tittmann, Physiol, Uilters. ueb. Callus* 

 bilduiJg an Steoklingen holziger Gewachse. Pringsheira^s Jahrb. 

 f. wise. Bot., 1895, Bd. XXVII, p. 164, 



