590 Wisconsin Academy of Sciences , Arts, and Letters. 
The experiments in which a; single white light was used 
afford some evidence as to the factors which influence the dis¬ 
tribution of the sporanges on the receiving plate. These fac¬ 
tors naturally fall into two classes: those which concern the 
structure and operation of the aiming and firing mechanism, 
and those which are external to the individual sporangiophore. 
Nearly all of the sporanges struck the glass immediately over 
the opening through which light was admitted, when the dis¬ 
tance from culture to opening was relatively short. Even in 
those cases, a few sporanges did not reach the opening but 
struck below, above or to one side. There is therefore some 
variation in the accuracy with which the individual sporangio- 
phores aim toward the source of light. This difference may 
result from an unequal sensitiveness of perception on the part 
of individual sporangiophores, or from a difference in the per¬ 
fection of the firing apparatus, or from a combination of both 
causes. It is probably to be traced back to some factors in the 
organism itself rather than to external conditions at the time 
of discharge. Whatever may be the cause of this variation in 
the accuracy of aim, it is apparent that it has an important 
bearing on the final results in all of the experiments. 
Not only is there a variation in the accuracy with which the 
individual sporanges are fired toward the light, but the force 
with which they are discharged is plainly quite unequal. Even 
at comparatively short distances, as we have seen, some of the 
sporanges fell below the opening; and at the greater distances 
individual difference in this respect stood out much more 
plainly. Some of the sporanges struck the opening even when 
the culture was at a distance of ninety-two centimeters,, al¬ 
though sixteen and seven-tenths per cent failed at this dis^ 
tance to reach the vertical glass and fell on the floor of the 
box. Variations in the force of the discharge, therefore, as 
Well as in accuracy of aim are to be reckoned with in the con¬ 
sideration of the final results. 
Our experiments have made it plain that the distance of 
the culture from the source of light is another deciding factor 
in the distribution of the sporanges. The number of spo- 
