Physiology of the Spermatozoa of Ferns . 581 
especially in view of the experiments of Pfeffer, if the starch 
has in general the significance here given it. 
The vesicle swells considerably during the swarm-period, 
and must occasion considerable resistance in the motion of 
the spermatozoa through the water. If, however, the starch 
is used up as food this disadvantage might be more than 
compensated, and the arrangement of the spermatozoid and 
its vesicle be likened to a locomotive with its well-stored 
tender attached behind. It is, however, possible that the 
vesicle may be partly used to regulate the motion or as a 
balancing apparatus during the swarm-period. One can 
scarcely suppose that so comparatively large a structure is 
a useless vestige of the mother-cell. 
V. Summary of the Chief Results. 
In addition to malic acid and its salts many organic and 
inorganic salts widely occurring in cell-sap give the sperma¬ 
tozoa of Ferns a positive chemotactic stimulus. 
Malic acid and its salts attract more strongly than any 
other substances tested. 
It is not free malic acid, but may be one of its salts, which 
plays the chief role in attracting the spermatozoa to the 
archegonia. 
Sugars, alcohols, asparagin, and urea do not attract. 
The attracting neutral salts do not give an unmistakable 
tonotactic repulsion at high concentrations. If such a re¬ 
pulsion occurs it does not prevent the spermatozoa from 
finally entering concentrated solutions where they are brought 
to rest by loss of water. 
The repulsion given by malic and maleic acids is chemo¬ 
tactic. The dissociation theory of solutions gives a clue for 
understanding the chemotaxis of the spermatozoa. 
The attracting of the spermatozoa by cell-sap is not a 
decisive proof of the presence in it of malic acid compounds, 
and may take place in their absence. 
The withdrawal of a certain quantity of water from the 
