147 



of 'Cfiltis in the formation of callus. Also in roots rich in 

 parenohjnTia; cases are not lacking in which the i700d parenchyna 

 after 'injury takes part in this forimition, I have never as yet 

 been able to observe division in the wood parenchjoir. of roots 

 of Taraxacum. 



If we again look over what has been said, v;e oan make 

 certain that, after injury, the cambiu:^ and secondary bark, 

 corresponding to the normal dividing activity of the*^ onmbial 

 cells, strive to form a tissue radially arranged. In the 

 pith and primary bark of the objects investigated such a ten- 

 dency was not found. 



Petioles and leaves also often form abundant callus from 

 their bark' tissue and especially from their mesophyll. To me 

 the callus excrescences formed on the petioles of Populus 

 seemed especially striking because so abundant.' The oolofless 

 tissue formed on the edges of wounds of leaf blades (Acer, 

 Syringa, etc.) bears but slight resemblance to the normal epi- 

 dermis with which it has been comixired at times by various 

 authors. The life history of the^ callus on leaves discloses 

 nothing new. The extensive callus rolls deserve especial men- 

 tion, however, which are produced in the leguminaoeous cotyle- 

 dons, rich in starch, after their removal from the axis, I 

 found them becoming highly multicellular in Vicia"*-. Here th© 

 cells- below the cut surface are also elongated perpendicularly 

 to it and divide repeatedly without noticeable regularity , 



In fleshy leaves, the burrows Beaten into the mesophyll 

 by insect larvae are not infreouently filled by a mu3bti cellular 

 callus, containing chlorophyll, which distends the epidermis. 

 Thus, in later stages, instead of the burrows, we fl^ fidgeS 

 on the leaf which are filled ^ith oellus. (Por exv.fmXe , in 

 Sedum spectabile, Brassica, etc), 



A thorough investigation of the changes to be found 

 in leaves injured by mining insects might well be ^orth 

 (164) while. The conditions aoting Jiere on the injured tissue 



differ essentially, however, from those which oome tjto 

 effect after somewhat coarse interference on the P^p J^ 

 the experimentor. Perhaps the reaction of the plant tis- 

 sues is also correspondingly different. 



The filling of the burro^-s ^dth callus tissue is 

 shown also by the tender masses in the wood of different ^ 

 trees, long known as "moon-rlngs" . According *o ^^^^J^ ® 

 description, thev are composed of irregulaily polyhedrio 

 parenchyma cells with thick liltted walls arranged Irreg- 

 uaariy. On account of their similarity to medullar y-tiB~ 

 sue, Nordlinger called them "medullayy spots". Their his- 

 tology, the irregular arrangement of their elements^ ana ^ 



"1" Since" van" TiQgham'(iReoh' s. X. g^jf^i^St-i^^ ,-5l?J: J°;« 

 Wn+ ■Rftf f5W6 qA* 1873 T XVII. p. 208) whose statements 

 shoiia1rowa-he«; thefate iAhe isolate* eotyledonB 

 has been especially investigated. 



^ Further statements on callus in leaves also in Massart 

 IOC. cit^fBlaokroan and Matthael:- On *,^^,-«^^f VVsSS 

 traumatic stipxilat ion. Ann. of Bot,, 1901, Vol. J^«-5;.^xSei:ee 

 Merhold Ueb. d. Sprueh -u. Buerrfleokenkrankh. d. Steincbstee, 

 landw. Jahrb!; 190i; Bd. 322, p. V?! and many others. 



3 Vergl. Anat. d, Veget. ^ Org,, V* ^07. 



