155 



cuttings of the poplaiftB, elms etc., which usually develop 

 numerous "Lohden redges" from the ^; llus*. Further, there 

 are plants which produce new vdget tlve p'olats directly from 

 the cells of their permanent tissue as well as by the mediation 

 of callus tissue; for Instance, Begonia leaves after rerooral 

 from the stalk and injury to their rihs, produce new shoots 

 and roots directly from the epidermal cells as well as from 

 the callus t issue , produced on the edge of the injury on the 

 3.eaf .. It has never as yet been observed in higher plants 

 that the cells exposed on the surface of the wound would have 

 been able to produce a new vegetative point, withoiit the in- 

 terposition of callus .tissue. 



The consideration of these regenerative processes is only 

 loosely connected with "pathological anatomy", in as much as, 

 in the formation of root or shoot vegetative pointy, the pro- 

 ducts of abnormal tissues is stopped by the formation of nor- 

 mal ones, Nevertheless a few remarks concerning the foima- 

 tlon of c rr.- ^^? in callus may well be added here. The fact 

 that meriwStematic complexes in the form of shoot or root vege- 

 tative points can arise from the cells of the callus tissue^ 

 is one of its most important characteristics. 



Callus occurring on injured roots may be just as capable 

 of forming organs as that on pieces of the stem and on leaves. 

 Yet in most plants not all organs seem to be able to form new 

 vegetative poihts from their callus; in man3r others the ability 

 to do this is lacking in the callus of all organs''^, - or per- 

 haps we are ignorant of the conditions under which the callus 

 tissues of these pl8,nts may develop vegetative points. 



Up to the present the callus tissues of poplar cuttings 

 have been the most oarefujly Investigated as to their ability 

 to form adventitious organs. If they are placed in the usual 

 way in water, in a few weeks a large number of adventitious 

 shoots are developed from the callus. Thus it is shown, that 

 light has no influenoe on the formation of the latter. Natur- 

 ally adventitious -shoots sprouting the lark have the character 

 of etiolated ones. Further it is shovm, that cuttings, of 

 whioh the apical ends are immersed, form adventitious shoots 

 on the basal poles, which extend into the air. According to 

 Tittmann roots may be produced from the bdsal poles of poplar 

 'cuttings, when placed under water. 



The root-pieces of Taraxacum which form callus behave sim- 

 ilarly in regard to the formation of shoots. As has been said; 

 when kept in moist air, they form their callus preferably on 

 (173) the basal pole, (the one toward the root neck). Placed inver- 

 ted in the water, sand or plaster, the apical- pole as well 

 forms callus and adventitious shoots with equal luxto-iance. It 

 is indeed possible to cause these pieces of roots which hrve 

 formed callus and adventitious shoots on the sprouting pole, 

 supplementarlly to form a second callus and a second series of 



^ Further examples of fieverinck. Over het outstaan van 

 knoppen en wortels uit bladen. Nederl. Kruitk, Arch., 2. Berie^,, 

 deel III, p. 458. Reohinger (loc. clt.) and others. 



^ According to Hansen, Vergl. Untersuch. uebdr Adventiv- 

 bild bei Pfl. Abhandl. Senckenberg, Haturf, Ges. 1881. Bd. XIX. 



^ In leaves which grow roots after separation from the 

 axis, these roots are very often produced not from the callus, 

 but above the cut surface. 



