852 



thread in the sapwood (Fig. 202, j) is examined, it is found that the broad 

 vessels are filled with a brown gummy mass in which are crystalline precipi- 

 tates of calcium carbonate (^) ; the contents of the wood parenchyma and 

 medullary ray cells surrounding the vessel are deep brown and the adjoining, 

 narrower vessels (e) are filled with tyloses. Starch is found only in the 

 sapwood ; in the heart wood, instead of the starch, brown grains are found 

 which turn to bluish black with ferric chlorid. Stoppages of the vessels r.re 

 not found in the sapwood but only in the heart wood. They are caused 

 primarily by tyloses, which occur exclusively in the inner heart wood, while, 

 in the outer heart wood ring, stoppage by gum or calcium predominates. 

 Often whole row^s of vessels in summer wood are filled with calcium, usually 

 in the carbonate but at times in the oxalate form (Fig. 202, 4). The calcium 

 carbonate, deposited in the youngest parts of the heart wood, is dissolved 

 later. In the same way, the great amount of gum in the sapwood disappears 

 with the change to heart wood. 



The tissue next to the wound surface in a horizontal wound dies back, 

 more or less. In the living tissue immediately underlying this, the vessels 

 are stopped up by means of gum, farther back by the formation of tyloses. 

 The fact that the vessels have drops and layers of gum only on the parts 

 adjoining the wood parenchyma cells, while the gum is lacking when they 

 adjoin neighboring vessels, proves that it is the wood parenchyma cells 

 which excrete the gum. The changes which characterize the heart wood 

 begin much earlier on wound surfaces than on normal uninjured trunks, 

 extending backward, however, only so far as the wound stimulus was effec- 

 tive. On this account, it is termed "wound heart wood," by some observers 

 "false heart wood" in order to distinguish it from true heart wood. Many 

 bacteria are found near the cut surface but not in the deeper part of the 

 various centres of heart wood formation, beginning at the wood surface and 

 extending as light brown tissue stripes through the sapwood. Since the 

 disease agrees in appearance with Gummose hacillaire, it is understood to be 

 an immediate result of injury in older parts of the trunk. This wound 

 stimulus may act chiefly on the protoplasm of the wood parenchyma cells 

 surrounding the vessels ; ^t may be continued further because of the con- 

 tinuity of the protoplasm of adjoining cells and may incite the wood paren- 

 chyma cells to a premature formation of tyloses. These cells, therefore, 

 grow old and die prematurely. The normal secretion of gum, at first very 

 abundant, ceases with the formation of tyloses. The process described is 

 made clearer by an examination of the accompanying figures. 



In Fig. 202, ^ (an alcohol preparation from a ten-year branch of Vitis 

 riparia), j indicates the boundary between two annual rings; m,m medullary 

 rays, g, gum cells, g' vessels with strongly contracted gum contents. At the 

 right (Fig. i), are reproduced two gum cells from a one-year-old shoot of 

 Vitis vinifera (blue ToUinger) ; their contracted gum contents are seen in 

 the centre. Only the inner outline of the cell walls is drawn. Fig. j is the 



