824 



Here too j to j indicates the line .of the cut ; all below this is callus 

 formation, which has pushed out the thick rolls from the original cambium 

 and spread over the cut surface from its outer edge inward. In the longi- 

 tudinal section shown in the figure, we distinguish a roll (ca) cut through 

 radially and a callus (ca'-), projecting outward from the back edge and then 

 cut across, the bark of which has already united with the laterally incurving 

 ca. Thus, in this older rose cutting at any rate the pith is covered but this 

 takes place by the union of edges, curving in from the periphery toward the 

 centre, while in the Fuchsia cutting illustrated above the main mass of callus 

 is formed by the pith itself. 



The indication of the various elements agrees in general with that of 

 the preceding drawing, m is the pith, which was here torn when cut. The 

 cut (ii) has been filled with callus projecting out from the back edge; h is 

 the old wood, formed before the branch was cut ofif ; nh, the new wood 

 formed during the period of propagation, exactly corresponding in character 

 to the new wood of the callus in the grapevine. This begins with short, 

 wide, porous, thick-walled cell masses, rich in starch, in which occur like- 

 wise short reticulated vessels. Their elements become narrower and nar- 

 rower toward the outside and more elongated, more and more resembling 

 the normal ones the later they are formed after the cut is made, i. e. the 

 closer they lie to the cambial zone cc. This cambial zone extends around 

 the cut surface of the old wood in broad curves and is covered on the optside 

 by the newly formed bark (nr) w^hich is not completely reproduced in the 

 drawing. We notice on the outermost edge of the bark the corked and 

 (lying first stages of callus (a), extending at first over the cut surface and 

 formed of broad, spherical to pear-shaped cells, arranged in rows, the end 

 cells of which are rounded. These cell rows are increased at first at the 

 ends, since the outermost cells have enlarged and been divided by cross walls, 

 and the small end cells thus reduced in size repeat the process when growing 

 further. 



In the callus roll {ca"), which extends from the back outward, and has 

 been cut transversely, g indicates the short reticulated vessels, which rcprc- 

 sert the beginnings of the new wood. Around this extends the cambial zone 

 (c'). b is the old phloem strand, formed before the cutting was made. It 

 has been pressed far away from the old wood at the cut surface by the 

 abnormal new wood formation, and has died at its free end. The cells lying 

 against both sides of the phloem fibre groups have been released from the 

 sap pressure by the cut and have stretched transversely (/), while in a 

 normal condition they would be elongated. The remaining outer part of 

 the old bark (r) has not changed and has closed the wound with cork, o 

 indicates the rhomboid, isolated crystals and stellate druses of calcium 

 oxalate. 



The new roots grow sometimes from the callus itself, sometimes from 

 the basal regions of the cutting above the callus, according to the plant 

 species. 



