570 Bidler*—Contributions to our Knowledge of the 
It was ingeniously proposed by Pfeffer 1 to use sperma¬ 
tozoa as a test for malic acid in the cell-sap of plants. He 
brought broken cells into a medium in which spermatozoa 
were swimming, and found that the latter were attracted 
by the diffusing cell-sap. He therefore concluded that malic 
acid was present in the cells. Since, however, it is now 
known that many other substances widely occurring in 
cell-sap such as tartrates, potassium oxalate, phosphates, 
&c., attract spermatozoa at fairly low concentrations (yJ-q- 
mol), this test for malic acid in cell-sap cannot be con¬ 
sidered decisive. 
The cell-sap of a petiole of Gunnera scabra 2 contained, 
according to an analysis of de Vries: 0-56 gm°/ 0 of sub¬ 
stances containing the negative radicle of malic acid, 0-67 
gm°/ o potassium chloride, o-oi gm °/ 0 potassium phosphate, 
and 0-56 gm °/ 0 glucose. Such a cell-sap would undoubtedly 
attract spermatozoa. The chief role in the attraction would 
be played by the malic acid compounds. The potassium 
chloride would, however, also attract strongly. The glucose 
would have no action whatever. 
Another analysis of de Vries showed that the growing 
point of the stem of Helianthus tuberosus contained 0-91 
gm °/ o potassium nitrate. This is sufficient to cause a strong 
attraction, as is evident from Table I. From the cases of 
Gunnera , Helianthus , and others which cannot be quoted here, 
and from the fact that many substances determined to give 
a positive chemotactic stimulus, such as tartrates, oxalates, 
potassium salts, &c., occur very frequently in plant-cells, 
we may conclude that the attraction given by any cell-sap 
is not necessarily due to malic add compounds, and may 
take place in their absence. 
Pfeffer determined an attraction by the cell-sap of all the 
plants (about thirty) which he employed for his experiments. 
The plants included Algae, Fungi, Mosses, Ferns, Gymno- 
1 Pfeffer, loc. cit., Bd. i, p. 413. 
2 De Vries. Eine Methode znr Analyse der Turgorkraft, Jahrb. f. wiss. Bot., 
Bd. xiv, 1884. p. 574, 
