30 
Journal of Agricultural Research 
Vol. XI, No. r 
4. ON THE ROOTS OR CAMPHOR TREKS 
Thus far no definite evidence exists that Tylenchus penetrans seriously 
injures the camphor tree. It was found in small diseased areas on the 
feeding roots, but not in such numbers as to seem to be the cause of 
trouble. 
NUMBER OF HOST PLANTS 
As a rule a given parasite infests but few hosts. In the genus Tylen¬ 
chus and a few related genera, there are some marked exceptions to this 
rule, one of the most astounding of which, Heterodera radicicola , infests 
nearly 500 different species of plants. Not long ago in this Journal 1 at¬ 
tention was called to another species, Tylenchus similis, which infests 
such widely different plants as the banana and sugar cane. Tylenchus 
penetrans is another addition to the already rather formidable list of 
Tylenchi that infest a number of widely different plants; and a glance 
at the list of hosts just recorded warns us that we need not be surprised 
to find it infesting almost any of our crop plants. 
IDENTIFICATION 
As there are a number of Tylenchi closely resembling Tylenchus pene¬ 
trans, no nema should be assigned to this species unless its anatomical 
details clearly correspond with all those given herein. The features that 
should be examined with special care in making comparisons are: Tip 
region; spear and median bulb of the esophagus; location of the excretory 
pore; the almost complete absence of wings; 2 the form of the tail, espe¬ 
cially that of the male; and the size and general proportions of the body. 
These latter, however, may vary to some extent in accordance with the 
age of the specimen, and in the case of the females, according as they are 
or are not in a gravid condition. Some nemas, while keeping the relative 
proportions of many of the different parts, vary considerably in size, so 
that some specimens may be twice as long as others. 
LOSSES 
No definite information exists as to the full extent of the injury caused 
by this parasite upon cotton and camphor. In the case of violets the 
losses consist of failures, and poor growth resulting in inferior bloom. 
Such losses may reach an amount that constitutes a very serious 
handicap. 
Present information indicates that the losses in the case of potatoes may 
sometimes be serious. The potatoes that reach a salable size often have an 
inferior appearance that detracts roughly 10 to 20 per cent from their 
market value, or even more. The infested tubers are inferior in size 
1 Cobb, N. A. tylenchus similis. the cause op a root disease op sugar cane and banana. In 
Jour. Agr. Research, v. 4, no. 6, p. 561-568, 2 fig. 1915. 
8 These are too strongly emphasized in figure 1. 
