143 



amount of callus is produced by the cambium on pieces of stem 

 or stalk^. In many oases indeed this is the only tissue 

 which ^s able to produce it. Next to the cambium, the prim- 

 ary and secondary bark tissues, as well as the pith, come un- 

 der consideration, which can also furnish considerable amounts 

 of tissue - often the activity of the bark is scarcely less 

 than that of the cambium. 



I'li^ formation of callus therefore furnishes proof that 

 Sirough injury, not only meristematio tissues, such as the 

 cambium, ban be brought to an increased and abnornrl activity, 

 but the cells of the permanent tissue as well, such as bark 

 and pith, can be incited to extensive growth and abundant 

 division, 



life history of the oallug 



The life Mstory of Irhe callus will have to be studied 

 separately In the various t issues producing calluses. As a 

 basis of our description, we will take first of all the phen- 

 omena 45bserved oh tsuttings -of woody planta. 



The impcrtont part playe4 by the cambium in the calltffi 

 /-,,r«x i°*'"'*''*^°'^ which has just been ment toned, has been thoroiighly 

 (158) investigated by Stoll {loe. clt.) with cuttings of Passiflora 

 quadrangular is . "Aft«r the lapse of 24 hours the cjross wall^ 

 oi -cue camoiax cjells, bordering the out surface and previously 

 flat, had become^ cur Ved outwfefd,- when not cut to pieces. A 

 stretching parallel to the lo»g axis took place simultaneously 



with thi6 outward ctitving, and after 84 hoiirs more, a division 

 over the cut surface by means of two or thlroe cross walls". 

 Further, "in the cambium a region <Jf cells, capable 6f contin*- 

 ually forming others by tangentixil and cross^diviflion, Kskd 

 been^ differentiated over the cut surface^ whicTi formed the 

 point of departure for all further growth from the cambium; 

 The cells lying below this point undertook no nev; division, 

 and were pushed away .little by little toward the outsidd". 



The Investigations fif Stoll (loo. clt.), R. Hoffman^ and 

 others, as well as my own, show that tlie cambial cells when 

 dividing after injury, are not restricted to the mode of normal 

 division but ar© capable of growth and divisitMi in every direc- 

 tion. It ia certain therefore that the changed pressure condi- 

 tions are of great significance. On the other hand it i& 

 scarcely possible to explain by these alone the phenomena of 

 growth which follow in;)ury^. The cell divisions leading to 

 the formp,tion of callus are very regular in those woody plants 

 which form it quickly and abundantly. Therefore the processes 

 are in detail as follows. 



If cuttings of Populus pyramidal is and others are placed 

 in water and covered with a bell glass, so that the upper end 



^ Knowing the significance of the callus fot the tmion 

 of scion and stock, it is thus comprehensible, that plants with 

 a cambial ring unite more easily when brought together, than 

 plants without one (monoootyledons) , 



„ ^ Hofftaan, Rob, Unters. ub, d, Wirkung mechanisch. 

 Krafte auf d. Teilung, Anordnung und Ausbildung d. Zellen u.s. 

 w. Dissertation Berlin,. 1885. - Schumann, Di eke nwaohs turn u. 

 CambiiJm Dissertation Breslau, 1873, 



3 



Compare R, Hoffman, loe, clt. 



