

PLANT DISEASES 397 
mission of one of the so-called virus diseases of plants may occur through the 
medium of plant parasitic nematodes. 
Just how the lesions of red ring in the cocoanut are produced by Aphelen- 
chus or how the similar disease in Africa may be caused by Diplogaster, or 
indeed how the other plant diseases result in which different species of A phelen- 
chus or Tylenchus have been encountered, is not at all clear. Cobb has pointed 
out that it is by means of a sharp onchus or spear lying in the pharynx and 
extruded from the buceal orifice that the invasion of the plant by some of these 
parasites is specially made possible. 
In red ring, the lesions consisting of softening of the tissues, their lique- 
faction and subsequent necrosis are apparently not of a nature that one can 

No. 336. — Diplogaster sp. from Cocos nucifera 
reasonably attribute to nematodes alone. In no pathological condition of 
which we have knowledge are such necrotic lesions produced by parasitic worms. 
We have earlier called attention to the fact! that in “red ring”’ bacteria 
are very frequently associated with the nematodes in the lesions and have 
suggested that the bacteria, often probably introduced by the nematodes, 
may play an important part in the destruction of the tissue. 
So far as we have been able to ascertain, nematode invasion or infection of 
Cocos nucifera has not been previously reported from Africa. We are not able 
to say whether the relative scarcity of coconut trees along the Liberian Coast 
is to some extent due to this disease. Linder, on page 522 has referred to the 
preventative measures to be taken regarding the spread of ‘‘red ring.” 
Mandioca mosaic. <A disease of the mandioca plant (Manihot palmata) is 
very common throughout Liberia and parts of the Belgian Congo. We noticed 
1 Strong: Relation of Certain ‘‘Free Living’’ Saprophytic Microorganisms to Disease. Science 
(1925), LXI, 97. 
