FIELD WORK IN PLANT PATHOLOGY. 107 



ample, in the determination of the amount of injury from smut 

 in barley. A correspondent, a trained scientific man, estimated 

 the amount of injury in a given case at 15 per cent., but an 

 actual count showed only 10 per cent injury. The methods 

 used in cases of this sort will serve to illustrate the quantitative 

 method and may be presented more in detail. The writer has 

 used three different methods for making the count; the staked 

 quadrat, the hoop method, and the quadrat frame. The observer 

 with full freedom of choice as to location of quadrats is hardly 

 likely to obtain accurate results. The hoop method in its ease 

 of manipulation has some advantages, but my preference is given 

 to the use of the quadrat frame. The quadrat frame is a light 

 wooden frame enclosing a square yard and provided with cross 

 wires which divide it into smaller squares. The observer ad- 

 vances into the smutted field, throws the frame out before him, 

 and then counts the smutted and unsmutted heads in each 

 square. The estimate is made from at least three such counts, 

 with due allowance for the extent to which unsmutted heads of a 

 smut-infected plant have been reduced in size. 



In many other cases the extent of the injury cannot be 

 made in this way, but can only be detennined with the harvest- 

 ing of the crop. Sorting and grading the yield give fairly 

 quick and accurate returns for many of our annual crops. Rust 

 injury of wheat or injury of potatoes from early blight may 

 serve as illustrations iji this class. Sorting and grading the yield 

 is often the sole method employed in determining injury in the 

 case of perennial plants. We have a good illustration of this 

 in the case of estimates of apple scab injury, where the effect of 

 the disease on the foliage, and consequently upon the general 

 tone and future productiveness of the tree, is almost forgotten. 

 In other cases the yield is not affected in a direct and striking 

 way, and consequently an immediate determination of the ex- 

 tent of injury is impossible, thus making necessary a continued 

 series of observations extending over years. 



The next line of field work for the pathologist to which I 

 would call your attention is experimental and demonstration 



