May 3, 1924 
Dissemination of Tylenchus dipsaci in Seeds 
477 
SEEDS OF OTHER PLANTS LIKEWISE NEMATODE CARRIERS 
The dissemination of parasitic stem nematodes undoubtedly takes place by 
means of the seed of other composites and allied plants in a similar manner. 
Reference has already been made to the observations of Maige (8) in Crepis 
taraxacifolia. Geisenheyner (1) described a gall due to “Anguillulides ” in 
Cirsium bulbusom in which the swelling is situated at the base of the flower head. 
(3, No. 5915, p. 1016), as it is in Hypochaeris and Taraxacum in America. A like 
condition exists with Leontodon incanus , in which the “Tige est epaissie et 
tordue, au-dessous de Tinflorescence, sur un longeur de 20 mm. et plus/’ etc., 
according to Houard (3, No. 6048, p. 1036). Likewise, in Hieracium pilosella 
“Capitule gonfl6 et contourn6 demeurant ferm6, ports sur une hampe florale 
renflSe.” (Houard, 3 , No. 1698, p. 1057). In all probability the seeds of all 
these plants are penetrated by the nemas, without injuring their capacity of 
being carried by the wind. 
In Dipsacus fullonum , a member of the family Dipsaceae, which is very close to 
the Compositae, the same manner of dissemination undoubtedly occurs, as 
already cited (5). Ritzema Bos (12) mentioned infestation in onion seedlings 
(Allium cepa) in the earliest stages of their development. A large part of this 
was due to the fact that penetration had taken place from infested soil shortly 
after the appearance of the cotyledon through the seed coat. In addition, 
however, he found Tylenchus dipsaci in the blossoms of mature plants, and in 
one case 3 per cent of the seeds were infested. In many other plants whose seeds 
are not windblown it is possible that the nemas enter the seed and are carried 
with them. 
Dissemination of the plant parasitic nematodes on the surface of seed undoubt¬ 
edly takes place to a large extent as well. This will be treated at length in another 
paper in connection with experimental work on the clover and alfalfa stem 
nematode. 
SIGNIFICANCE OF WIND DISSEMINATION OF THE STEM 
NEMATODE 
It is too early to make any estimate as to whether or not this great spread of 
the stem nematode in the composites may be of any economic significance. 
Indeed, any disease that even suggests the possible lessening of the spread of 
either the false or the true dandelion might be looked upon as a blessing rather 
than otherwise, except possibly in connection with the few fields of cultivated 
Taraxacum grown for food. Thus far the indications are that the nemas infesting 
the composites are specialized physiological races not capable of infesting others 
of the known economic host plants. There are indications of gradual adaptation 
to new host plants, however. Further investigations are being made in this 
connection. 
SUMMARY 
(1) The leaf and stem infesting nematode, Tylenchus dipsaci Kuhn, has been 
found to be abundant on the false dandelion, Hypochaeris radicata , along the 
Pacific coast, from Tacoma, Wash., to San Francisco, Calif. It occurs as well 
in the true dandelion, Taraxacum officinale , in Western New York, the Province 
of Ontario, Canada, and at Boston, Mass. According to the literature, it occurs 
abundantly on these and other composites in Europe. 
(2) In addition to producing swellings and distortions of the leaves, the nemas 
penetrate the developing flower head and produce more or less distortion in that 
region. Furthermore, in the case of the false and true dandelion they were ob¬ 
served to have actually penetrated into the interior of the seed. 
(3) This accounts definitely for their wide distribution on these hosts, for 
the wind carries the nematode-infested equally well with the nematode-free 
seed. 
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