476 
Journal of Agricultural Research 
Vol. XXVIII, No. 5 
point of attachment with tl\e receptacle. These were found to contain nematodes. 
The eelworms could readily be seen with the binocular coiled up in the interior, 
through the semitransparent achene wall, as shown by Plate 2, A. Seeds in 
more advanced stages of development were found, upon dissection, to contain 
living nemas. One showed a nema extending from the base. Another (PI. 2, B) 
showed one at the upper extremity, at the base of the pappus stalk. Some of 
the seeds were killed by the invasion, as shown by their completely collapsed con¬ 
dition. In some of the invaded seeds, however, such injury did not occur, for 
the seed was intact, since the eelworms were present only between the achene 
wall and the testa of the seed. 
Experimental plantings of seed from diseased flower heads produced a reduced 
stand of seedlings, among which were several typically diseased plants. Swellings 
appeared first in the petioles of the primary leaves, and subsequently in one or 
two of the permanent leaves. Plate 2, C, shows one of the affected seedlings 
with characteristic swelling in the midrib of the first secondary leaf. Examination 
of such a plant three days after infection was first evident disclosed larvae of 
Tylenchus dipsaci not yet quite sexually mature. In all invaded seed observed, 
the pappus was apparently normal and the seed capable of being transported by 
the wind. Plate 2, D, shows several mature seed of Hypochaeris radicata. Some 
of this same lot were later shown to contain living nemas. 
In the true dandelion ( Taraxacum officinale) exactly the same conditions ex¬ 
isted. The leaf symptoms are identical with those previously described for 
Hypochaeris radicata. Plate 3, C, shows typical leaf swellings. Plate 3, A, 
shows one of many nematode-infested heads found, this one sectioned to show the 
discolored receptacle and seed bases. More than 50 per cent of the seed in this 
particular head were invaded by nemas. One of the seeds with its pappus is 
pictured in Plate 3, B. The seed is undamaged in spite of the fact that a nema¬ 
tode was present beneath the outer seed coat. 
A study of growing plants made it evident how primary invasion of the seed 
head takes place. Both Taraxacum and Hypochaeris grow as a “rosette” on the 
ground, with flat leaves radiating from a common center. The outer ends of 
the leaves often are higher than the inner, thus permitting dew and rain to flow 
in toward the center, carrying with them free nemas that have migrated out of in¬ 
fested spots in the leaves. Tylenchus dipsaci was thus observed many times 
in the young,, actively growing central region of the plants, some of them free 
from the host tissues, others within the young, highly susceptible parts. Without 
doubt much of the leaf infection takes place when the leaves are young. It is 
likewise in this region that the flower heads form and develop. Ready infestation 
of the flower head can thus take place, and, indeed, many young heads were 
observed that were thus infested. Plate 3, D, a photograph of a dandelion plant 
sectioned longitudinally, shows two flower heads in different stages of develop¬ 
ment, and their obviously favorable location, when young, for infection by nemas. 
The well-known rapid growth of the pedicel after the flower is fully ^ed is 
a factor which favors the dissemination of the invading parasites, as well as of 
the seed, by the agency of the wind. 
It is evident that dissemination of the nemas by the seed is easily accomplished, 
and under natural conditions it undoubtedly takes place to a large extent. If 
the seed has been killed, the eelworms released may still infest plants that are 
already established. If the infested seed is alive then a new colony is established 
at once, with the host plant immediately available. Thus is explained the dis¬ 
tribution of the nematode parasite to an extent that is practically coequal in 
range with that of its host, the false dandelion, in the Pacific Coast States, and 
the probably widening circle of infestation in the true dandelion in the Northeast. 
