329 



Iree appeared a yellowish green and juicy. It consisted of bark parenchyma, 

 which had originated from a healthy cambium. 



The subjoined Fig. 46 



t.. 



pictures the bark about \.o 

 be shed. At h is shown 

 the old wood; at nh the 

 last produced new wood ; 

 g indicates ducts ; c the 

 cambium. Next this lies 

 the normal, young bark 

 which gradually passes sp. 

 over towards the outside 

 into the broken older bark. 

 In reality the extent of 

 loosened older bark is 

 much greater in proportion 

 to the normal young bark 

 than is shown in the draw- 

 ing, because of lack of 

 space. The normal inner 

 bark has a very regular 

 structure, in which layers 

 of porous bark parenchyma 

 alternate regularly with 

 flat bands of slender cells 

 (/) which might be differ- 

 entiated as "wedge-cells." 

 These slender cell bands 

 would correspond to the 

 "pressure wedges" men- 

 tioned in connection witli 

 the tan disease. The cells 

 forming these wedges ap- 

 pear in longitudinal section 

 as long as in cross-section, 

 nearly colorless, with pe- 

 culiar, wide-meshed wall 

 thickenings, looking like 

 irregular wedges. The 

 parenchyma lying between 

 every two such thin, slen- 

 der bands of wedge cells is 

 proportionately large-celled, porous and rich in starch. Deposited in it 

 are large, hard bast bundles, {h) with the rows of calcium oxalate crystals 

 accompanying it (0) and the cells {si) containing mucilage. 



TTlSt 



Fig'. 46. Elm bark with barlv excrescence. (Orig.) 



