. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . ch the majority of the species have a preference for comparativelycold water, although they are often very erratic in their appearance. 430 Ecology M. stagnorum, Tribonema ajjine is not uncommon in peaty ponds and species of Ophioci/tiam are very common in stagnant pools, especially0. majus and 0. parvulum. Species of Tribonema are not common in thetropics and occur mostly in elevated areas, but the genus Ophiocytium isquite a
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . ch the majority of the species have a preference for comparativelycold water, although they are often very erratic in their appearance. 430 Ecology M. stagnorum, Tribonema ajjine is not uncommon in peaty ponds and species of Ophioci/tiam are very common in stagnant pools, especially0. majus and 0. parvulum. Species of Tribonema are not common in thetropics and occur mostly in elevated areas, but the genus Ophiocytium isquite as abundant as in any temperate region. Most genera of the Hetero-kontte like shaded pools or those which are grass-grown at the belonophorus and Botrydiopsis arrhiza occur as rare constituentsof the alga-flora of small ponds, although the former has been found in theplankton of lakes. The Peridiniese of small ponds and ditches are not particularly commonest form in western Europe is most probably Peridinium cinctuinalthough several species of Gymnodinium are frequent. c Apr Tflay June July Auy Sef>t Oet Hov Dec. Fig. 268. Estimated relative importance of the several types of algal periodicity and the com-position of the alga-flora at any time of the year in the waters of eastern Illinois. Theirregulars are not depicted. (After Transeau.) Fritsch (06) suggested a division of small pieces of water into two series: a. Those containing Cladophoracew, in which the water is to a great extent fairly well aerated. b. Those from which Cladophoracew are absent, in which the aeration is much less. There is no doubt that the presence of perennial species of Cladophorahas not only a marked effect on the alga-flora of a pond but on the annualcycle of that pond. There is, of course, always a struggle between Cladophoraand its epiphytes, and this is not much affected by the presence of otherAlgse. These epiphytes are, however, not confined to Cladopho
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