Oct. i f 1917 
New Parasitic Nema 
3i 
as well as in quality, so that the yield is materially lessened. When 
the parasite infests the roots, as well as the tubers, it may cause an actual 
falling off in the number of tubers that are formed. 
MUSCULAR POWERS: PENETRATION 
When removed under the surface of water from potato pustules, the 
nemas sometimes lie so loosely in the tissues that they fall out three or 
four at a time with every movement of the dissecting needle. The 
structure and general appearance of this parasite discountenance the 
idea that its body movements are very active, at any rate after entering 
the host tissues. Specimens removed from potatoes exhibit only slight 
and weak movements. 
The oral spear and the median bulb of Tylenchus penetrans are so well 
developed as to indicate clearly that the parasite is one readily capable 
of forcing its way into the tissues of the host plant. This fact will be 
appreciated by comparing these features with the corresponding features 
of other destructive species. 
CONTROL 
One important preventive measure is at once suggested by the 
presence of this parasite in the tubers of the potato—namely, great care 
in the selection of seed potatoes. 
So far as potatoes are concerned, the problem of combating Tylenchus 
penetrans is very similar to that of combating the ravages due to Hetero - 
dera radicicola; the essence of it may be summed up in the old saying 
that “an ounce of prevention is better than a pound of cure.” In this par¬ 
ticular case it might almost be said that “an ounce of prevention is better 
than any amount of cure;” or rather, attempt at cure, for there is no 
assurance that land once infested with these nemas can ever be cleared 
of them. In the case of the average parasite, infesting but a single host, 
rotation of crops offers a solution in many cases at once effective and 
comparatively inexpensive. When, however, the parasite is capable 
of sustaining itself on a variety of hosts, especially if common weeds are 
among these hosts, the rotation of crops may not prove a thoroughly 
efficient remedy. It may be that no paying crop that is immune 
can be found. Even if such a crop exists there is the ever present menace 
that the parasite may maintain itself in the roots of weeds, difficult and 
expensive to exterminate. These facts strongly emphasize to potato 
growers the advisability of being very careful to plant nothing but 
perfectly healthy tubers. 
An examination of potatoes treated with mercuric chlorid for scab 
showed that this treatment has a certain value in killing Tylenchus 
penetrans in the tubers. The scabby potatoes were also infested with 
7 \ penetrans . The vitality of the nema was much reduced and many of 
them appeared to have been killed by the mercuric chlorid. 
