Nov. 6, 1916 
Host Plants of Thielavia basicola 
297 
certain cases on stems above the surface of the ground has been noted 
by others (11, 14), but is relatively rarely found. The lesions obtained 
on Portulaca oleracea were almost wholly on the low succulent stems, 
apparently irrespective of any infection at the base of the stem. Ordi¬ 
narily, however, infection occurs only on the roots of the host plants or 
upon the base of the stem just at or below the surface of the soil (PL 18). 
In the case of Nicotiana spp., infection is ordinarily found on the sec¬ 
ondary roots, although in some species the collar of the plants may be 
most markedly injured, whereas in the cucurbits the infection is usually 
on the stem just at or below the surface of the soil (PL 18, fig. A). In 
species of Pisum, Phaseolus, and Lupinus the fungus was ordinarily 
found first upon the base of the stem or on the primary root (Pl. 18, 
fig. C). On pansy ( Viola tricolor) and phlox, where only very slight 
infections occurred, they were invariably found at the ends of the smallest 
fibrous roots. 
The character of sporulation seemingly differs mostly in the variation 
of the appearance of the perithecial stage. Many workers have expe¬ 
rienced failure or considerable difficulty in locating this stage and have 
therefore questioned the connection of the perithecia as described by 
Zopf with the chlamydospores of T. basicola . The association of the 
perithecia upon a large number of the different host plants observed in 
these tests with the chlamydospore stage of T . basicola is fairly con¬ 
vincing as to the correctness of Zopf’s conclusions. The perithecia 
were found to be especially abundant upon Cucumis maxima , Robinia 
pseudoacacia , Cytisus scoporius , Nicotiana tabacum , and to a lesser 
extent upon a number of other hosts. Although it can not be so stated 
with certainty, the perithecial stage is apparently never produced in 
the same way on some host plants, as it is lacking in pure cultures of 
the fungus. The size, shape, number, and color of chlamydospores 
produced upon the various hosts differed to some extent. These differ¬ 
ences appear to be determined in part by the location of these spore 
chains. When formed within the host cells, as is common in certain 
hosts, they were often restricted in their growth and were malformed. 
In other hosts such as Cucumis spp. and Linaria spp. they are com¬ 
monly formed outside of the host cells and are large and uniformly 
shaped. The color of the chlamydospores varies from a deep blue-black, 
as on species of Cucumis, to a light brown, as on species of Nicotiana. 
The conidial spore form is only rarely seen on the living host, although 
it is produced early and profusely in culture media. 
The addition of a large number of new host plants of T. basicola , 
while working with a comparatively small number of species, is taken to 
mean that the range of host species may perhaps be again doubled in 
time. Although its pathogenicity was questioned by earlier workers, it 
is shown that these conclusions were drawn from limited data and that 
these investigators used species which were either immune or relatively 
