CORRELATIONS 



333 



vascular bundles originated, connecting the portion inserted and the main root, 

 and after a short time it was possible to determine only at certain places (gg in 

 Fig. 100, /) where the transplantation had occurred and to observe there a 

 demarcation between the graft and the stock. Similarly we may cut out a 

 cortical block from a branch and replace it, allowing healing to occur. The 

 amalgamation takes place if a sufficient number of protoplasmic cells capable 

 of growing be present ; if these be absent, as in old wood, amalgamation is 

 impossible ; if these cells are present only in one region, e.g. in cambium, a local 

 amalgamation alone is possible. 



If now the part cut out be inserted into the wound with different orientation, 

 if, for example, it be turned inside out or upside down, amalgamation still takes 

 place; but after a longer or shorter time a pathological condition ensues, for there 

 develops a swelling which in extreme cases may bring about the death of the plant. 

 The factor concerned in the tumour is polarity, which is functional in every cell and 

 not only longitudinally but also radially. [Miehe (1905) has demonstrated this 

 polarity in individual cells of Cladophora in a very beautiful manner.] If we com- 

 pare a plug of beet inserted in the orthodox manner (Fig. 100, /) with one inserted 



m 



Fig. i(X). Mode of growth of transplanted portion of 

 beet. /, tangential section through the upper end of a 

 portion of tissue inserted in the normal orientation. The 

 limits of the tissue are indicated by the dotted lines gg. 

 The longitudinal lines indicate vessels. //, a similar section of 

 an inverted graft. The vascular bundles are developing almost 

 entirely in the long axis ; 1 and // about natural size. ///, 

 individual cells from the area of fusion ; /, intercellular spaces 

 and thickened cell-walls. X about 350. After VbcHTING, 



lessels 

 from Cydonia japonica. 

 One is united to the other 

 by an intermediate curved 

 vessel. X 120. After 

 VdCHTISC, 1892. 



upside down (Fig. loo, //) we see that in the latter case the continuity of the 

 vascular system is destroyed, the polarity of the vessels is altered in so far that 

 their basal ends are unable to unite with the distal ends of those already present 

 in the stock. The new formations attempt to bend round and lay themselves side- 

 ways against older vessels so that they orientate themselves in the same direc- 

 tion. Fig. loi shows more exactly the mode of union of the vessels, the polarity 

 of which is indicated by arrows. By no means all cells are able to effect an 

 accurate junction ; the disturbance caused by the severance is permanent, 

 and hence arises an active growth leading to a hypertrophy, suggestive of the 

 effect produced by the attack of a parasite. 



Similar results are produced when we plant a piece of tissue cut out of a 

 certain region in another situation. It is possible to transplant in the same 

 way a portion of tissue on another individual of the same species or on another 

 species. Only experiments which aim at transplanting a portion of tissue 

 bearing one or more growing points are of especial interest. Such transplanta- 

 tions are frequently carried out in gardening operations, as when budding or 

 grafting of small twigs is resorted to. The part transplanted is spoken of as 

 the graft or ' scion ', and that to which the graft is attached as the 'stock \ In 



