4*8 
Journal of Agricultural Research 
Vol. IX, No. i* 
showed that the germ tubes produced by R5 are constantly smaller than 
those of the remaining strains. Figure 3 illustrates this relation. The 
writers consider this character the most reliable in the identification of 
these strains. In making the measurements of the germ tubes the ques¬ 
tion arose whether different length germ tubes produce tubes of varying 
width and also whether the size of the sclerotial cell is correlated with 
the size of the germ tube. In order to determine this point, 100 meas¬ 
urements were made of the short sclerotial cells, the length of the germ 
tube, together with the width of same. The results may be summarized 
as follows: The size of the cell has no apparent effect on the length or 
width of the germ tube; nor has the length of the germ tube any appre¬ 
ciable effect on the diameter of the germ tube. The width of the germ 
tubes produced by the germinating enveloping sclerotial cells of R5 vary 
from 3.4 to 6.8 n, with an average of 4.3 /x, while those of R7 and R4, 
taken as representatives of the remaining strains, vary from 6.8 to 11.9 
/x, with an average of 8.5 /x. 
Table I summarizes the measurements made in the above comparative 
studies. 
Table I. —Comparative measurements of strains R$ and R7 of Rhizoctonia solani 
Diameter of 
mycelium. 
Sclerotial cells. 
Diameter of 
germ tubes. 
Length. 
Width. 
Rs 
R? 
Rs 
R? 
Rs 
R? 
Rs 
R 7 
M 
M 
M 
Minimum. 
4. 7 
IO. O 
13 - 6 
17. 0 
8.3 
11. 9 
3-4 
6.8 
Maximum. 
8.8 
14. O 
30. 6 
6l. 2 
20. 4 
23-3 
6.8 
11. 9 
Average. 
00 
rL 
IO. I 
21. 6 
37-5 
12. 3 
16. 7 
43 
8- S 
Comparison with Rhizoctonia crocorum (Pers.) DC.—Duggar gives 
the mycelial measurements of R. crocorum (Pers.) DC. as 4 to 8 /x; of R. 
solani Kuhn, 8 to 12 ju. According to the measurements of the writers, R5 
varies from 4.7 to 8.8 /i and the common strain of R. solani from 10 to 
14 fi. These measurements agree so closely with those of R. crocorum 
and R . solani as given by Duggar that there appeared to be need for a 
closer comparison with R. crocorum. Such a comparison was made with 
exsiccatae material, with material of R. crocorum on asparagus collected 
in Germany by Dr. H. A. Edson, of the Office of Cotton, Truck, and 
Forage-Crop Disease Investigations, and kindly furnished by him to the 
writers,'and lastly with the descriptions and distinguishing characters 
as outlined by Duggar. 1 Unfortunately, the original specimens from 
which the isolations were made were not saved, as at that time it was not 
known that the strain of Rhizoctonia isolated was essentially different 
1 Duggar, B. M. Op. cit. 
