5/1 



I could observe other stages of healed frost blisters in the maple and 

 the apple. As yet the best examples have been found m the maple, and, in 

 fact, on two year old shoots, more than 1.5 m. long. Many of these, in 

 their whole course, excepting the tip region, and on all sides, showed small 

 flat, completely bark covered bosses, possibly 0.5 mm. high which were 

 more noticeable to the touch than to the eye. The outer bark appeared 

 perfectly normal and the direct continuation of the remaining, not rough- 

 ened part of the branch. In cross-section, the cause of the out-pushing of 

 the bark may be recognized in the swelling of the wood body which, at the 

 beginning of the second annual ring, has formed an aggregation of paren- 

 chyma wood cells very broad and rich in starch. As a rule, such an 

 aggregation of wood parenchyma is found lying exactly between two 

 medullary rays so that the lateral transition from this diseased wood tissue 

 to the healthy tissue is rather sudden, while the abnormal wood elements 

 assume very gradually in a radial direction the normal dimensions and 

 thickness. Only in the radially and laterally adjacent wood with a regular 

 structure are found greatly widened and shortened wood cells filled witli 

 starch (investigated in May). 



In the wood parenchyma aggregations, irregularly extended, yellow- 

 stripes are found; the yellow color arises from swollen cell walls which are 

 universally present in frost injuries. Also, other characteristics of a 

 definite group of frost injuries are present as, for example, the lateral dis- 

 placement of the medullary ray cells at the frosted place and the barrel- 

 shaped widening of the medullary ray where it enters the parenchyma 

 aggregation. This barrel-shaped widening of the medullary ray is pro- 

 duced less often by the increase of its cells than by their broadening at the 

 expense of their length. In this, not infrequently, a very striking thicken- 

 ing of the secondary membrane is noticed. Cell increase is found most 

 frequently in the one-celled medullary rays which, from the point injured 

 by frost, become two-celled. The further such a medullary ray extends 

 into a parenchyma aggregation, the broader and shorter its individual cells 

 appear in cross-section and with relatively more slanting walls ; they dove- 

 tail into one another, instead of remaining bluntly placed against one 

 another. At last the shape of all the cells in the parenchyma aggregation, 

 of which the elements are widest near its centre, become the same so that 

 no difference can be recognized in the medullary rays. 



A brown bark zone, tangentially elongated, which was formerly con- 

 nected with the parenchyma but is now separated by newly interposed 

 wood, corresponds in the same radius to the yellow or brown striped 

 aggregations of parenchyma wood. 



By coloring the section with campeche wood extract, very interesting 

 pictures are often shown, if a concentrated solution of chloriodid of zinc 

 is added. The difference in thickness in the walls of the wood cells 

 becomes more apparent. The walls of some groups of wood cells are 

 colored more intenselv yellow and are more swollen. 



