98 



of tyloses after injury (according to Wieier) . We may 

 therefore consider tyloses as callus-hypertrophies of the 

 "bark and other tissues. Like these and other hypertrophies 

 tyloses also, as I have convinced myself by experiments 

 with Platanus cuttings, are furthered in their developement 

 "by the action of air rich in moisture. 



On the other hand, it ts well known that the formation 

 of tyloses may occur in very, many plants, even without 

 previous injury. In the heart-wood and in ageing sap-wood 

 the ducts are filled with them, !Ehe' question must remain 

 undecided whether •^\''. in heg-tt-wood, etc., similar factors 

 act upon the parencjiyma cells, as' " when branches are 

 cut off, or in any kind of injury, or whether other condi- 

 tions than these, effective after injury, can cause the 

 formation of tyloses. The tyloses, independent of the 

 woiiSid stimulus, appear, however, not only in ageing parts 

 of the trunk, hut also in organs still very young; for 

 esaample, in the Cucurbitaceae , The conditions which cause 

 tylose formation in ageing organs seem therefore to be ful- 

 filled occasionally in young ones also. 



There are still other statements, according to which 

 attacks by parasites exert an influence on the tylose for- 

 mation. Tylose formation is said to appear after infection 

 by fungi. 2 



In order to be able to explain uniformly, the 

 production of tyloses in wound-wood and in heart- 

 wood, Bohm assumed that the filling of the ducts 

 with air, under the usual pressure, is the cause 

 of tylose formation. Molisch (loc- cit. p. 295) 

 has criticised this assumption; "In an injured 

 branch, tyloses are formed bery abundantly perhaps 

 1/4 to 1 cm. below the wound, somewhat farther 

 down markedly less frequently, until finally 2 to 

 (105) 3 cm. deeper they do not appear at all. If the sus- 



1. Wiler, Ueb. d. Ahteil d. sekund. Holzes der dikotyl. 

 Gev;. an d. Saftleitung, etc. loc. cit. Fort the formation 

 of tyloses after the falling of the leaves , see Staby JJ'^-'^. 

 d. Verschl. d. Blattnarben nach Abfall d. Bl. Flora, 1883, 

 Bd. LXIX, p. 113. von Tieghera and Guignard, Observat. s. 1. 

 mecanisme de la chute d. feuilles. Bull. Soc. Bot. Srance 

 188B, T. XXIX, p. 312. Tison, loc. cit. Therein also fur- 

 ther bibl. Weber (Ueb. d. Einfl. hoh. Temperat. auf d. Fah- 

 igkei^t d. Jlolzes, den transpirationsstrom zu leiten. Ber. 

 |, B. Bot. Ges. 1885, Bd. Ill, p. 345) obtained tyloses in 

 Ihe vicinity of piaces of branches which had been killed by 

 heat, 



£. Compare for instance, Mangin, Sur la maladife du Rouge 

 d, 1. pepinieres etc. C. R. Acad. Sc. Paris, 1894, T. CXIX 

 p. 753 (Beob. an Ulnus and Ailanthus nach Infection durch 

 U0ctria cifinabarina) . Brillieux and Delacroix. La gomose 

 bacillaire, maladie des Vignes. ANK, Inst. Hat, Agron. 

 |.g95, T. XIV. 



