Physiology of the Spermatozoa of Ferns . 555 
salt. The repulsion R is protective, for it prevents the 
spermatozoa entering too deeply into the acid substances 
and thus becoming injured. The slight repulsion which 
occurs during an attraction by a neutral salt is, however, 
not protective, for the spermatozoa finally enter too deeply 
into the tube, where they are immediately brought to rest 
from loss of water. 
The repulsion R from the acid substances is undoubtedly 
chemotactic. If it were tonotactic, sugar, asparagin and 
neutral salts should repel when tested at concentrations 
isotonic with repellent solutions of the acid substances. 
A comparison of the data given in the tables makes it evident 
that this is not the case. The repulsive effect which is 
to be observed during a marked attraction by a neutral 
salt may on the other hand be tonotactic. If so the tono¬ 
tactic repulsion is very slight and easily overcome by the 
chemotactic attraction. 
The term N has been used to indicate that no collection 
takes place in the tubes at the concentrations isotonic with 
1 mol potassium nitrate. A collection in these cases appears 
to be mechanically impossible. If a substance attracts, 
e. g. potassium nitrate, the spermatozoa may collect in the 
diffusion-zones outside the mouth of the tube. On approaching 
the mouth, however, the spermatozoa come to rest owing 
to the withdrawal of water from their protoplasm. They 
cannot at best penetrate more than one diameter into a tube, 
and when they do so are slowly carried out again by currents h 
Solutions isotonic with 1 mol potassium nitrate are com¬ 
paratively heavy. In consequence they fall with apparent 
rapidity out of the tubes. This phenomenon prevents the 
collections of spermatozoa in the less concentrated diffusion- 
zones from being clear. With a solution of \ mol potassium 
nitrate the collection outside the tube may be definitely 
observed. At the beginning of the experiment the sper¬ 
matozoa may penetrate 2-3 diameters down the tube before 
1 The outgoing stream on the bottom of the tube and into which the spermatozoa 
fall after coming to rest. 
