. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . absent, multiplication of individualstaking place only by the formation of zoogonidia or motile gametes. Theplants are mostly coenocytes and unseptate, with a gregarious habit. This1 Previously known as the Endosphaerine tendency. Phylogeny of Isokontse 150 line of evolution has resulted in no Green Algse of importance, and like theVolvocine series has not emerged from the confines of the Protococcales, unlessBlackmans suggestion as to the or
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . absent, multiplication of individualstaking place only by the formation of zoogonidia or motile gametes. Theplants are mostly coenocytes and unseptate, with a gregarious habit. This1 Previously known as the Endosphaerine tendency. Phylogeny of Isokontse 150 line of evolution has resulted in no Green Algse of importance, and like theVolvocine series has not emerged from the confines of the Protococcales, unlessBlackmans suggestion as to the origin of the Siphonales is a correct one(see p. 223). The tendency to retain the unicellular or unseptate form inthe adult plant and to restrict multiplication entirely to small motile cellsis found in the Chlorochytriese, Dicranochseteae, Characiese and small groups have therefore been placed alongside one another in thefamily Planosporaceae. A similar multiplication also occurs in the coenobicHydrodictyacea?. The evolutionary lines within the Protococcales may be represented asfollows: Siphonales ^ --U ^ ? 7 ? Hydrodictyacese. Palmellacese O o O oo HO PSPu. Chlamydomonas A careful consideration of our present knowledge of the Isokontse leadsone to the conclusion that there are only six natural groups into which itcan be divided. These groups, both for convenience and for the sake ofconsistency, are here termed orders, and are as follows : Order 1. Protococcales. 2. Siphonales. 3. Siphonocladiales. 4. Ulvales. 5. Schizogoniales. 6. Ulotrichales. 160 Isokontae Order 1. PROTOCOCCALES. The Algae of this order are mostly unicellular, motile or non-motile, or lessfrequently simple coanocytes. The cells are often aggregated to form looseirregular colonies and are frequently embedded in a copious mucilage. In a fewforms there is a definite coenobium1, which may be a coanobium of coenocytes,but a definite multicellular thallus does not occur. The order includ
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