2 9 



Bunder the microscope, till the idea occurred to me to stain the 

 whole transverse section of the wood with a solution of iodine. 

 By this process it was very soon possible to obtain information 

 as to the distribution of starch in the wood : the starch-containing" 

 wood turned a blue-black ; that containing none, a yellow- 

 brown colour. I can recommend this very simple method to all 

 who feel inclined to continue research in the direction I have 

 indicated. 



The result of the examination was most interesting. I begin 

 with the bark. 7 Above the cut, starch was abundant, more so 

 than higher up on the stem. Only quite close to and above the cut 

 in a zone 5 cm wide was it in small quantity. The same was the 

 case beside the upper end of the wound. How starch is other- 

 wise distributed in the basal parts of the stem, will be seen best 

 from the diagram, in which I have set forth my discoveries 

 according to very exact measurements. Wherever the organic 

 substances, uninfluenced by the tapping, had been able to descend 

 vertically, quite as much starch was found as above the upper 

 spiral curve. Below this curve, however, that is, wherever the 

 organic substances had been forced to move sideways or obliquely, 

 a considerable decrease in the quantity of starch, commencing from 

 the upper end of the tapping cut, was very soon noticeable. 

 However, the existence of starch could still be proved in the 

 spiral strip of bark between the wounds, at a distance of half 

 the tree's circumference from the upper end of the incision 

 (measured parallel with the wound). Starch was com- 

 pletely absent from the other parts of cortex and 

 bast at the stem's base. By a treatment with Fehling's 

 Solution there was no difference noticeable between the reducing 

 sugar-forming property of the bark that contained starch, and 

 that which contained none. 



The distribution of starch in the bark corresponded entirely 

 with that in the outer layers of wood : wherever starch was 

 entirely absent from the bark, or present only in a small quantity 

 the same condition existed in the outer, 2 cm thick, layers of wood. 

 Right at the upper end of the incision in a transverse sect inn 

 marked (a) in diagram 2.), starch, as in the case of the hark, 



~ ( By bark I mean hen- as well as on the |>re<eeilin- pa;;e. \vhirh 

 I daresay has already been noticed, bark in the ordinary sense <>t tin- 

 word, and bast. 



