F. H. Stewart 
175 
We now proceed to the consideration of: 
C. The route taken by the parasite on the host during 
IMMIGRATION FROM THE SOIL. 
There are two views on this subject: (1) that the parasite, having entered 
the host plant below the level of the ground, ascends through the tissues of 
the stem to the leaves (Ritzema Bos, 1893, and Marcinowski, 1908-1910); 
(2) that it enters through the surface of the leaf, having reached this situation 
by travelling over the surface of the plant. 
(1) Ritzema Bos (1893) found Aphelenchi in apparently healthy leaf-stalks of Begonia 
and Asplenium. In an experiment with an infected Pteris, he cut off all the parts of the 
plant above ground; the young fronds which grew up contained Aphelenchi, and he con¬ 
cludes that they came from the interior of the rhizome; it is, however, equally probable 
that they came from the surface of the soil. Marcinowski (1908) found a few Aphelenchi 
in the stem of a plant. The two observations of Aphelenchi in the stem appear to have 
been made by dissection or teasing; in such a method it must be borne in mind, that worms 
lurking on the surface may appear in the medium, and it may be thought that they have 
issued from the tissues. I have found a few Aphelenchi on teasing up portions of flower 
stalk, but on cutting serial sections have never found them actually in the stalk or stem; 
in one case I divided a groundsel stem longitudinally in halves, one half was teased out in 
water, and numerous adults and larvae found, the other half was cut into serial sections, 
but no Aphelenchi were found in the tissues, although several appeared on the cut surface. 
The following observations also are offered to this view: the parts of an infected plant 
below the leaves are healthy (Klebahn, 1891); plants placed among infected leaves, if pro¬ 
tected by a ring of vaseline around the stem, remain free of the parasite (Marcinowski, 1908); 
if all diseased leaves are removed from a plant, the buds growing out of the axils remain 
free (Molz, 1909). 
We can therefore conclude that Aphelenchi, in their invasion of the host 
plant, do not traverse the tissues of the stem. 
Aphelenchi in the soil, revived hy moisture, and attracted by a suitable 
plant, wander on to it, and may live for some time as ectoparasites in the leaf 
axils before reaching their definitive habitat in the mesophyll. 
In order to trace the course of immigration, I placed a number of young 
plants of groundsel ( Senecio vulgaris) in pots of earth, on the surface of which 
infected leaves of Chrysanthemum and Lomaria had been strewn. The pots 
were kept in a room at a temperature of 10-15° C. (50-60° F.), were freely 
exposed to the sun, and were watered once daily. Entire plants or leaves 
were examined at intervals with the following results : 
2nd day. Four entire plants negative. 
3rd day Three plants examined. Plant (a): on syringing out the leaf axils with water 
three adult males and four females were found; in a leaf touching the ground—one adult 
female. The earth in this case had been infected 44 days previously, and had been 
bare of vegetation for some hours before the planting of plant (a). Plant (6): in a leaf axil 
one adult, on a leaf one larva, 0-305 mm. long. The earth had been infected 43 days pre¬ 
viously, a chrysanthemum which bore ectoparasitic Aphelenchi was growing in the same 
pot. Plant (c): negative. 
