1906] FULTON—CHEMOTROPISM OF FUNGI 105 
intimately associated with chemotropism, and that many of the tests 
for the latter are in equal measure tests for the former, direct tests 
were made by growing the fungi in media of higher osmotic pressure 
and of lower osmotic pressure than the test media, as well as in an 
isosmotic medium; glycerin, a good nutrient substance, and yet a 
substance reported by Mryosut to be neutral in its chemotropic 
effect, was used to give the desired concentration to the culture 
media. The series failed to show that the concentration of the 
culture medium has an effect upon the amount of turning. How- 
ever, no excessively high concentrations of mineral salts were used. 
Other tropic phenomena.—Under conditions that would favor a 
manifestation of geotropism and of thigmotropism, there was no 
indication that these are concerned in determining the direction of 
growth of the fungi. The effects of light and of heat were in no 
way tested, but they probably do not enter as factors. 
Biological significance—The conclusions reached in these studies 
may be found to have a somewhat important bearing upon the 
biological problem of infection by parasitic fungi. In the absence 
of any experimental investigation, nothing definite can now be said. 
It would seem, however, that the drying of dew and other surface 
moisture in which spores had gerimnated, might be a condition 
favoring the hydrotropic turning of the germ-tubes toward the 
stomates, especially if the cells within are over-distended with water, 
which has frequently been observed to be a condition favorable 
for infection; if the germ-tubes are numerous in the vicinity of a 
stomate, the repellent influence of these upon one another would 
Cause some to seek the unoccupied region within the stomate. At 
all events the phenomenon of the entrance of germ-tubes, whether 
by way of the stoma or through the cuticle, is a complex one, of 
which many factors remain undetermined. That mere entrance is 
probably not due to specific peculiarities, either of host or parasite, 
is evidenced by the recent work of Miss Grsson which has been 
mentioned by MarsHatt Warp (33). Miss Grsson found that 
Spores of various members of the Uredineae sent their germ-tubes 
readily into the stomates of plants widely different from their hosts, 
and which they were unable to infect. MARSHALL WARD met with 
numerous instances of the same phenomenon. This would indicate 
