Physiology of the Spermatozoa of Ferns . 567 
potassium nitrate. If the concentrations are doubled so that 
they become isomolecular with the solutions in Table III 
attraction still takes place at the new concentrations. Sodium 
malate attracts therefore in solutions isomolecular with f x Fji 
! x too> i x ToVo> I x TF0TU- m °l malic acid. The free acid 
however, while attracting at the two latter concentrations, 
repels at the two higher. Sodium hydrogen malate and 
maleic acid behave in a similar manner. Common to these 
three acid substances in solution is the ion H + , whereas in the 
neutral salts it is absent. One would suppose, therefore, that 
the ion H + is responsible for the repulsion. 
If however the ion H + is the cause of repulsion, we might 
also expect to find that other acids such as tartaric, oxalic, and 
citric repel. This supposition I have not as yet verified. I was 
able tcf satisfy myself that these three acids do not attract, but 
remained in doubt 1 whether they repel or are chemotactically 
indifferent. According to Pfeffer 2 , however, citric acid repels. 
From his work with Bacteria, &c., he came to the conclusion 3 
that repulsion by acids at sufficient concentration is a general 
phenomenon. Jennings has found that Paramecium is re¬ 
pelled by all acids at the necessary concentration. We have, 
therefore, considerable support for the supposition that the ion 
H + is the cause of repulsion from acids. 
Reference has already been made to the ring-collections 
which may be obtained in an experiment with a strong 
solution of malic acid. A ring-collection is due to the fact 
that malic acid attracts at low concentrations and repels at 
higher. The part played by the ions may perhaps be ex¬ 
plained in the following manner. At 0 03 °/ o malic acid (see 
1 At this point in the research the material unfortunately became attacked by 
a Fungus, and in consequence the spermatozoa available for any given preparation 
were not numerous enough to decide the question. A repulsion is easy to observe 
when there is also an attraction because the spermatozoa collect in the intermediate 
diffusion zone. When there is no such attraction a repulsion must undoubtedly 
be much more difficult to observe. When Bacteria are used the detection of 
a repulsion with a substance that does not attract is much easier owing to the 
enormous number of individuals one may employ. 
3 Pfeffer, loc. cit., Bd. i, p. 387. 
3 Ibjd., Bd. ii, p. 659. 
