An examination was made of the influence of atrazine, simazine, malathion and 2,4-D on total chlorophyll produc tion by Chlorella vulgaris, Ch/orococcum hypnosporum, Sfigeoc/onium fenl/e, Tribonema sp. , Val/cheria geminata and Oscil/aforia lulea.The herbicide 2,4-D in concentrations up to 100 mg/I did not alter chlorophyll production by the algae. Ch/O/·o coccum was not influenced by the pesticides . When added individually, atrazine, simazine and malathion inhibited chlorophyll production at a concentration of I mg/I or greater except for Sligeoc/onium, in which production was not influenced by I mg/I simazine . Results were variable when the pesticides were present individually at a con centration of I fig/I. The three pesticides stimulated chlorophyll production by Chlorella when present individually at 0· 1 and 0·5 fig/I. The same was true for simazine and malathion on Tr ibonema and Oscillaloria. A complete examination was not made for all the algae in these lower concentrations of pesticides. A significant interaction was present among atrazine, simazine and malathion. Combinations of two pesticides resulted in more inhibition, less inhibition or stimulation of chlorophyll production depending upon the con centrations used.Treatment of Va ucheria with 1 fig/I malathion caused a production of brown crystals inside the cytoplasm, a formation of a second cell wall inside the first and distortion of gametangia developing at the time of initial treatment.
SUMMARY
Aphanizomenon flos‐aquae has been introduced into unialgal culture in a completely defined medium and maintained for more than 3 years in the colonial flake form found in nature. The color and size of the flake and general appearance of the cells are substantially improved over those found in the original material at the time of collection from Upper Klamath Lake, Klamath County, Oregon. The alga readily forms both akinetes and heterocysts in culture Bacteria‐free cultures have not been obtained.
A precipitate‐free medium designated ASM No. 8a has been developed from the ASM of McLachlan and Gorham. Their medium was altered by modifying the concentration of certain elements and by the addition of sodium bicarbonate, a 1/25 dilution of Arnon's trace element solutions B7 and C13, hydrogen ferric ethylenediamine di‐o‐hydroxyphenylacetate (EDDHA), and disodium ethylene dinitrilotetra‐acetate (Na2EDTA).
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