825 



The Utilization of the Various Axial Organs for Cuttings. 



Callus formation itself as we see is, therefore, the simple process of 

 healing a transverse wound. The formation of the cicatrization tissue at 

 the base of the cutting is aided by especially favorable conditions. Except 

 in healing the upper edge of the wound, the reserve substances in the cutting 

 momentarily find no other use than in the cicatrization of the lower wound 

 surface, since the usually shady place of propagation does not favor the 

 bursting of the buds. Where the growing conditions given the cuttings 

 through ignorance cause a rapid development of the buds, the formation of 

 callus and roots is reduced or fails entirely. In the second place, the moist 

 place of growth and the usually increased temperature of the soil act in 

 such a way that cell increase is favored on the lower cut surface, i. e. the 

 cicatrization tissue assumes a very luxuriant character. The formation of 

 callus is not absolutely necessary for the cutting. Plants, which very easily 

 produce adventitious buds, reduce their callus tissues to very small amounts. 

 They cover their cut surface by a formation of cork and utilize their reserve 

 substances at once for the formation and further development of new root 

 primordia. Here an abundant cell increase occurs only in the cambial zone, 

 lying immediately in the cut surface, whereby the base of the cutting 

 enlarges considerably (Begonia). The formation of callus can become very 

 injurious in trees which form, adventitious roots with difficulty, since by its 

 especially abundant development it consumes the material provided for the 

 formation of new roots. We find, at times, enormous knotty callus swell- 

 ings without any formation of roots (conifers). 



The kind and age of the cutting and the vegetative conditions given it 

 determine which tissue shall participate in the callus formation. The 

 cambium always takes part in this. Where it does not assume exclusively 

 the process of healing, it is assisted by the parenchyma of the inner bark, or 

 also by a part of all of the parenchyma of the pith. Further, even the 

 parenchyma of the wood and that of the older bark can participate in this. 

 In herbaceous, rapidly growing plants, even in their thick-walled elements, 

 a cell increase occurs near the cut surface because of the formation of 

 tyloses in the vessels and of a new formation of cross walls in the collen- 

 chyma of the older bark. It has been observed here ^ that the thickened 

 walls of the collenchyma cells and the vessels in the immediate proximity 

 of the tyloses swell up, become porous, and are, in part, re-absorbed. 



The more living parenchyma therein present, the more rapid and 

 abundant is the callus formation. The cuttings are generally made at a 

 node directly beneath a bud. In a cross section through a bud-cushion it is 

 found that the parenchyma mass is greatly developed here by the passing 

 over of the medullary connections into the bud. At the node the pith 



1 H. Criiger on Trinidad; Westindische Fragmente, XII. Einig-es iiber die 

 Ge'webesveranderung'en bei der Fortpflanzung' durch Stecklinge bei Portulaca oler- 

 acaea. Bot. Zeit. 1S60, p. 371. 



