PTERIDOPHYTA. 137 
The entrance of the living spermatozoid into the neck of the arche- 
gonium and its passage down to the egg is easily followed. In fact, 
the phenomenon is a matter of common observation in elementary 
classes. It is only necessary to mount prothallia with mature arche- 
gonia ventral side up in a drop of water, to which are added several 
clean male prothallia that contain ripe antheridia, and which have been 
kept in dry air for a short time previous to the operation. The ripe 
archegonia will open, and in a few minutes numerous spermatozoids 
which have escaped on being placed in the water will be found swim- 
ming about the opening of the archegonium, having been attracted 
thither by the extruded substance. Many enter the neck, and several 
may reach the egg-cell. The author has observed instances in which 
the number of spermatozoids endeavoring to enter the archegonium 
was so great that they formed a plug which almost completely closed 
the opening in the neck. 
Since the interesting researches of Pfeffer (’84) it has been known 
that the mucilaginous substance formed from the neck-canal and 
ventral-canal cells acts as a chemotactic stimulus upon the spermato- 
zoids. Pfeffer found that the spermatozoids of ferns are attracted by 
malic acid and its salts in very dilute solutions. A solution of o.oor grm. 
per cent. is sufficient to bring about a positive chemotactic reaction. 
Buller (1900) found that in addition to malic acid and its salts, many 
organic and inorganic salts, widely occurring in the cells of plants, 
exercise a positive chemotactic stimulus upon the spermatozoids of 
certain ferns. Among the organic salts which were found to attract 
are tartrates, potassium oxalate, potassium acetate and sodium formate, 
Among the inorganic salts are phosphates, sulphates, potassium nitrate 
and potassium chloride. Organic substances which were found to act 
indifferently are grape sugar, cane sugar, lactose, amylodextrine, 
glycerine, alcohol, asparagin and urea. ‘‘ Inorganic salts not appre- 
ciably attracting are the chlorides and nitrates of sodium, ammonium 
and calcium, and also lithium nitrate. Of the four free acids which 
seem to be most widely found in cell-sap, namely, malic, oxalic, tartaric 
and citric, only malic acid attracts.” The concentration of malic acid 
which gives the most pronounced reaction is 0.01 grm, per cent., 
while that which gave just an appreciable reaction was 0.001 grm. per 
cent, With potassium nitrate no attraction could be detected at 0.05 
grm. per cent., whereas there was a slight one at 0.1 per cent. 
Roughly estimated, therefore, malic acid attracts fifty times more 
strongly than potassium nitrate. Strong solutions repel. 
Attempts have been made to elucidate the phenomena of chemotaxis 
