. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . alstaking 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. Phytogeny of Isokontse 159 line of evolution has resulted in no Green Algae 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 correc
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . alstaking 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. Phytogeny of Isokontse 159 line of evolution has resulted in no Green Algae 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 coenobicHydrodictyacese. The evolutionary lines within the Protococcales may be represented asfollows: Higher Isokontse C^ * 1_ 1 O oipuu , tf ? 7 Planosporaceae Hydrodictyacese. ccacese Prot jcoccPalmellacese O o O oo 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 Isoko-ntx Order 1. PROTOCOCCALES. The Algae of this order are mostly unicellular, motile or non-motile, or lessfrequently simple coenocytes. 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 coenobium of coenocytes,but a definite multicellular thallus does not occur. The ord
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