. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . whole of the Green Plants. It may lie regarded as the phylogenetic Chlamydomonadese 173 starting-point of the various lines of (Jhlorophyceous descent. The history of these is ahistory of the intercalation of a vegetative phase between two successive motile (Chlamy-domonadine) generations, these motile phases being retained for reproductive purposes aszoospores and gametes ; in the oogamous types the male gamete alone remains motile, andconst
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . whole of the Green Plants. It may lie regarded as the phylogenetic Chlamydomonadese 173 starting-point of the various lines of (Jhlorophyceous descent. The history of these is ahistory of the intercalation of a vegetative phase between two successive motile (Chlamy-domonadine) generations, these motile phases being retained for reproductive purposes aszoospores and gametes ; in the oogamous types the male gamete alone remains motile, andconstitutes in the Archegoniate series the last remaining representative of the Chlamydo-monadine cell. The co-existence within the limits of an undoubtedly natural genus of the mostprimitive form of gamogenesis (the conjugation of equal clothed gametes) with agamogenesiswhich has the essential characteristics of true oogamy is also a feature of unique interest.(Blackmail & Tansley, 02.) As the genus is of such importance it has received considerable attention from anumber of investigators, notably Goroschankin (90—91), Dill (95) and Wille (03).. Fig. 102. Colourless members of the Volvocaceaa. A—D, Polytoma itvella Ehrenb.; B,formation of daughter-cells; C, fusion of motile cells; D, zygote. E and F, Chlamydoblc-pharis brunnea Franc£; F, division of cell. G, Tetrablepharis ijlobulus (Zach.) —F, after France, x 660; G, after Zacharias (from Wille). Two of the most interesting genera of the Chlamydomonadeae areBrachiomonas and Lobomonas, The first-named occurs only in submarinehabitats and possesses a cell-body furnished with five horns, all directed back-wards : one straight posterior horn, and four curved horns regularly disposedaround the antero-median part of the cell (fig. 101 A—F). These hornsare hollow outgrowths of the cell, the protoplast extending to their extremities,although the chloroplast generally does not. Lobomonas has only been foundin freshwate
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