bast bodies begin in the form of individual, short elements (hb) with wide 

 lumina and only later grow out from the cambium as connected groups of 

 elements (hb'^) elongated like fibres^^. 



The bark of the new structure has formed a protective cork layer in 

 its peripheral parenchymatous layers which has gradually grown very thick. 

 At first only plate cork was formed ; but later, in different places, full-cork 

 masses (Ik) developed instead of the plate cork cells, splitting the covering 

 (k) composed of the latter cells and pressing the cork cambium inward (kk) 

 by their increase which extends further and further backward. 



The full cork began to form when the whole peeled surface, for the 

 purpose of further investigation, was enclosed in a glass cylinder, partly 

 filled with water. While this lenticel out-growth, produced from the phello- 

 gen, was only slightly noticeable in those parts of the bark which remained 

 in the air, it had developed an unusual luxuriance below the surface of the 

 water. 



The tan disease of the cherry is therefore an abnormal increase of the 

 normal lenticel formation. So many and such extensive full-cork cushions 

 are produced close to one another that they unite, pushing off the epidermis 

 in large connected tatters and appearing as uniform velvety surfaces cover- 

 ing a large part of the branch. The outermost layers of the full cork cush- 

 ions are so loose that the connection between the peripheral cells is broken 

 by a slight blow when the air is dry; this explains the discoloration and the 

 dust flying from places affected with the tan disease, if the spots be touched 

 or shaken vigorously. This scattering of the dust increases with the num- 

 ber of full cork cells lying above one another and cushions composed of 

 parallel rows of full cork, 20 cells deep, have been observed. In this case 

 the process of elongation has included the entire thickness of the primary 

 phelloderm so that the later formed, secondary full cork lies directly under- 

 neath this, i. e., no separating plate cork layer is left between the difl:erent 

 generations. 



The appearance of the tan disease will have to be traced to the super- 

 ubundance of ivater in the bark body. This local excess of water may be 

 due, on the one hand, to supplying the roots abundantly with water, especially 



1 Reference should be made in passing- to the illustration of the beginnings of 

 tuber gnarls not in any way whatever connected with the tan disease but shown 

 in the drawing- at B. They are produced by a local accumulation of plastic material 

 as, for example, the isolated wood in the bark of the new structures formed near 

 the wounds of various trees (cherry, apple, pear and pine). At the centre of such 

 wood formations with a spherical wart-like structure may be recognized one or 

 more hard bast cells. 



The case in which hard bast cells (especially diseased ones) are overgrown by 

 tissue is of very frequent occurrence in injuries of very different origin. This over- 

 growth consists usually only of a covering of plate-like cork cells several layers 

 thick. In some cases, however, instead of the rapidly transformed cork cambium, 

 a persistently active cambial layer is formed which deposits wood elements toward 

 the inside and bark elements toward the outside. Such a case is represented in the 

 wart-like tissue excrescence (B) at (u') while at (u) in the left part of the figure 

 (A) may be seen only a cork covering around one of the isolated hard bast cells 

 first produced. The bark rays pass around these new structures on both sides as if 

 around some foreign body. 



