258 
STRUCTURE AND LIFE HISTORIES 
The' protoplasm appears to be streaming in a constant 
current in one direction, and this is thought to be due to 
the evaporation of water from surfaces more exposed to 
the air, and the intake of more water from the substratum, 
by osmosis. 
FIG. 185. Bread mold (Rhizopus nigricans}. A, older plant; myc, 
mycelia; sph, sporangiophore; sp, sporangium; st, stolon produced by A, 
and giving rise at its tip to a new plant, B. Greatly enlarged. 
261. Secretion of a Powerful Poison. In the course 
of some experiments, made in order to determine the 
cause of sex in the mucors, Blakeslee and Gortner in- 
jected into the ear of a healthy rabbit some of the juice, 
squeezed out of the mycelium of Rhizopus nigricans. 
To their great surprise the animal died almost instantly, 
before the injection was completed. Further experi- 
ments clearly demonstrated that Rhizopus contains a 
powerful poison (or toxin), which is soluble in water, 
but which produces its effect only when introduced into 
the circulatory system. When this expressed juice was 
fed to the rabbits, or when they ate the mycelium, no 
