33 2 Marshall Ward,— On a lily -disease . 
amounts to considerably more than a right angle, it seems 
to me impossible to avoid the impression that some attraction 
is exerted. 
I have tried to account for the phenomenon of the directive 
action as due to heliotropism or geotropism, but entirely with- 
out success ; indeed, I never met with a fungus which seemed 
more indifferent to light than does this one, and the direction 
of the branches seems to have nothing to do with the direction 
of gravitation. There are two factors, however, which do 
seem to be of importance when considering the whole question 
of the direction of growth and the fusions of the hyphae ; 
these are, firstly, the contact of hyphae with one another, or 
with a solid substance, and secondly, the direction in which 
the food-material lies with regard to free hyphae. Thus, as 
has already been pointed out, the contact of the young organs 
of attachment with the surface of the cover-slip stimulates 
them to exude ferment-substance and to branch, and the 
same is the case when they come in contact with the epi- 
dermis of a leaf or bud of a lily, with the difference that the 
exuded ferment there causes dissolution of the tissues, and 
the branching takes place in the dying mass of cells. In both 
cases, however, we have the irritation of contact first inducing 
accumulation of ferment at the spot, and branching follows. 
That one cause of the direction of growth of free branches is 
the presence of food materials is suggested by the mode of 
development of such mycelia as the one in Figs. 15 and 16, 
where the successful growth is all into the drop of culture- 
fluid, and similar directive influences are exerted by the tissues 
when once infected, as may be seen by the direct plunging 
in of the leading hyphae in Figs. 6 and 7, for plenty of evidence 
exists to show that these hyphae follow paths of least resistance 
prepared for them by a ferment in advance. Even in a culture 
liquid, and much more so in these cases, it may be a fair 
question whether the dissolved substances do not act as 
irritants keeping the ferment towards the tips of the hyphae, 
and if so there is no essential difference between the two cases 
so far. 
