344 Groom. — On Thismia Aseroe (Bee cart) 
reasons, because the currents in the cell set most vigorously 
towards the nucleus, and the hypha is carried with them, much 
as, in flowing water, a slender submerged stem has its young 
parts pointed down stream. The other possible explanation 
is that the hypha seeks the nucleus in virtue of its chemo- 
tropism, the chemotropically active substances being manu- 
factured or accumulated in greatest quantities nearest the 
nucleus of the infected cell \ This second explanation 
appears to be the correct one, as will be seen from the 
following considerations, (i) The distribution of the endo- 
trophic mycorhizal hyphae in a holosaprophyte suggests that 
we are dealing with a chemotropic phenomenon 1 2 . The 
coiled hyphae occur in some cells, but are absent from others 
equally accessible. They enter into cells of absorbing 
organs — roots, leaves, or stems — but avoid cells of organs 
which are not absorbing, whatever their morphological nature. 
And even in the absorbing organs the hyphae are absent 
from some cells (raphide-mucilage cells) though present in 
the contiguous one. (ii) Miyoshi 3 has shown that certain 
chemical bodies do exercise a directive influence on the 
hyphae of Fungi, (iii) There is evidence that absorption 
of plastic substances from the host-cell by the hypha 
takes place most vigorously near the nucleus of the cell. 
For in the mediocortex and limiting layer the bladders, at 
first full of protoplasm, form only in contact with the host’s 
nuclei. We cannot explain this local hypertrophy of the 
hyphae as due to a stoppage of substances conducted inside 
and along the hyphae ; because of the slender nature of the 
portions of the hyphae connecting the bladders with one 
another, and because of the early death and probably the 
complete occlusion of those portions. So we are compelled 
1 Of course it is equally conceivable that in one cell the hypha moves towards 
the nucleus in virtue of a repellent action of a substance which is consumed most 
rapidly near the nucleus. But, as will be seen later, this view would involve 
a number of complicated assumptions for which there is no evidence. 
2 Percy Groom, loc. cit. 
3 M. Miyoshi, Uber Chemotropismus der Pilze. Bot. Zeit. 1894. 
