1. Bracken spermatozoids are chemotactically attracted by malic acid salts and in a pH gradient aggregate between pH 3.5 and 5.6.
2. This response to pH occurs only when the sperm suspension contains malate.
3. At higher pH's, the response to an H+ gradient is as strong as the response to a malate gradient.
4. These observations suggest that bracken spermatozoids are sensitive to the bimalate ion rather than the malate ion. This is consistent with an earlier suggestion that chemotactic activity is associated with the cis-configuration, for the bimalate ion will have this configuration, while the malate ion and the malic acid molecule will have the trans-configuration.