of the mechanical eleraents,- the tuhers interpC; ated in the PBin 

 stock of the plants had to carry the weight of ^he parts of the 

 plant aBove ground. Accordingly, the tissue-formations here de- 

 scribed would have to he added to the list of activity hyper - 

 plasias . This explanation is undoubtedly very interesting, yet, 

 it seems to me that still other possible explanations should 

 (146) come under consideration here. The peculiar method of experi- 

 mentation lengthened the life period of the potato tubdr, -al- 

 ready emptied,- far beyond the normal one, so that a demand was 

 made upon the different tissues of the tuber for a very much 

 longer time than under normaX conditions, Evidently continued 

 demand does not of Itself mean the same as Increased demand. It 

 might well be possible that even "c ontinued " demand Is enough 

 under certain circumstances to IncT^e the abnormal formation of 

 secondary tissue, as observed by "Vochting. 



I would like here to call attention again to the experi- 

 ments of Meer-*' who found leaves cut from Hedera helix forming 

 roots and living for years. Secondary tissues were formed in 

 the petioles by which the vascular bundles originally separated 

 were united into a cord of tissue. It Is absolutely not pro- 

 bable that the new formation of duots etc. Is here to be traced 

 to an increase of the use of water, etc, To me the supposition 

 seems better founded, that the continued demand made upon cer-' 

 tain tissues, as a result' of an abnormally long period of life, 

 caused their hyperplastic formation. Yet to we not find that 

 many perennial plants in the normal development of their parts 

 under ground increase regularly, by eambial activity, their 

 tracheal and mechanical tissues, corresponding to a "continued" 

 demand made upon them, although the extent of the shoots devel- 

 oped yearly by them and the functional demand made upon them 

 by these remain approximately equal ^, 



In Vochting' s experiments, the conditions are in so far 

 the same that tissues determined by them were kept alive longer 

 than is usually the case under normal conditions. Here also a 

 "continued demand" is made, with which there is also connected 

 an "increased demans". The conditions are therefore extraor- 

 dinarily complicated. It will not be easy to decide whether the 

 reinforcement of tissues observed by vSchting in Solanus tuber - 

 osum , etc. are to be put on an equal footing with those des- 

 bribed by Mer or whether the "increased" demand was the deter- 

 mining factor of their production. 



Conditions are much simpler when It is possible to bring 

 about an abnormally abundant formation of vascular bundles in 

 organs witjjout lengthening the period of their life beyond the 

 normal, Vochting made experiments of this kind on dahlia tubers. 

 These ssrpre planted in an upright position and, in spite of the 

 unusual conditions, they rooted well, developing shoots in which 

 a part of the stem was replaced to some extent by a piece of the 

 root. Tubers, forced in this way to a greater mechanical work 

 and through whose vascular bundles the v/hole amount of water 



1 Bull, Soo. Bot, France, 1879, Bd, XXVI, p. 18. 



^ Increase of the tracheal and eventually also Of the me- 

 chanical elements, as a result of continued (not increased) re- 

 quirements, v/ill occur probably also in those one-year old plants, 

 whose shoots, used as stock, below the scion "become two or several 

 years old, (Compare Lindemuth, Das Verheilten durch Ropulation 

 verbundener Pflanzenarten. Ber, d. ]). Bot. Ges, , 1901, Bd. XIX, 

 p. 515), Unfortunately no suitable material has been accessilJle 

 for me to test this question. 



