ROOT-KNOT DISEASE OF TOMATOS. 



37 



degree of infection was adopted which we found suitable for indicating 

 changes occurring in the treated areas. When infected areas were 

 treated with sterilizing substances it was anticipated that at the end 

 of the season not a single nodule large or small would be found. Such 

 a result is marked — O. 



If, however, any nodule was found, say, of the size of a small 

 pinhead — I mm. diameter — the infection remained, and it had to be 

 marked accordingly. If in a io-foot length of bed from I to 6 nodules 

 were found of a size not greater than mentioned above, and located 

 in the soil immediately overlying the subsoil from which the eelworms 

 had travelled, or if these same half-dozen small nodules were found 

 in the subsoil, the infection was considered to be a trace — Tr. 

 (In no single case was a plant found with a few nodules near the 

 surface without having the lower roots covered with nodules.) 



If the nodules were more numerous, the next obvious difference 

 was between old nodules and young nodules. Where the nodules were 

 small up to J inch diameter, whitish in colour, succulent in appearance 

 and occurring on the deeper roots, a later attack of the disease was 

 indicated than would be the case where the nodules were large 

 (J inch to \ inch diameter), brownish in colour, and situated in the 

 higher as well as in the lower roots. Where the disease had been 

 heavily checked, only the smaller nodules, and these deeply seated, were 

 discernible. Where less than a quarter of the plants had these small 

 nodules the infection was marked X. 



Where less than a half of the plants had these small nodules the 

 infection was marked XX. 



Where old, brown, large nodules were found they indicated an 

 early attack by the eelworms, and it was to be inferred that the sub- 

 stance applied had shown little inhibiting effect even at the beginning 

 of the season. When old nodules were found in one up to a quarter 

 of the plants in the plot, the infection was marked XXX. 



Where more than a quarter of the plants on the plots showed old 

 nodules the infection was marked XXXX. 



Marks Tr, X, and XX are therefore distinguished from the others 

 as indicating a late attack, from which it was inferred that the applied 

 substance had at least formed a poisoned stratum for a time impassable 

 by the worms. 



Marks XXX, XXXX are alike in that they indicate an early 

 attack by the worms, and one would therefore infer that no appreciable 

 poison-stratum had been formed and that the worm-killing power 

 at the time of application had not been sufficiently great. 



This is summarized in the following table (II.) : 



XX 



o 



Tr 



X 



