112 Maine Agricultural Experiment Station. 1920. 



in no way restricted to plants grown in pots containing borax 

 or to plants included in the experiments under consideration. 



The size and rapidity of growth of many of the plants which 

 showed this type of injury in marked degree, particularly those 

 which were heavily watered, indicated considerable root growth 

 and this was confirmed by later examination. Likewise plants 

 which suffered severe root injury and stunting as the result of 

 heavy applications of borax showed relatively smaller amounts 

 of the tip and marginal injury. Therefore it seemed reasonable 

 to suppose that compounds of boron were being taken up by the 

 roots, were being carried along with dilute solutions of food 

 materials and deposited in the leaves. Since there is constant 

 evaporation of water from the leaves and a fairly constant cur- 

 rent of water from the roots upward through the stems and con- 

 tinuing through the leaves to the margins of the latter, it would 

 seem that any materials or salts brought along in solution in this 

 transpiration current, which were not used by the leaves in the 

 manufacture of food materials for tissue building or for storage, 

 would tend to concentrate most at or near the margins and that 

 this concentration would be greater in the older leaves. A suf- 

 ficient concentration of any poisonous material would result in 

 the death of the tissues at that point. 



To test the above assumption with reference to boron in 

 the plants in question some of the dead margins of the injured 

 leaves were removed with scissors. At the same time an ap- 

 proximately equal amount of the margins of healthy leaves was 

 obtained from plants which were grown upon fertilizer No. 5409 

 which contained no boron. These were tested qualitatively by 

 the Station chemist on December 3, or two months after the 

 tubers were planted. The sample from the injured leaves gave 

 a positive test for boron while that from the healthy leaves gave 

 a negative test. 



RELATION OF THE TIP AND MARGINAL INJURY OF THE LEAVES TO 



THE METHOD OF APPLICATION OF THE FERTILIZER AND 



WATERING. 



Based upon the larger series of pots with fertilizer 5549 

 where the applications of anhydrous borax were equivalent to 

 17.6 pounds per acre, fertilizer applied below the seed-piece, 



