. Plants and their uses; an introduction to botany . oming a resistant zygosporeready for a period of rest. The zygospore germinates b\- formingseveral swarm-spores (A) each of which in turn grows into a thallusas already described. In the sheath algae (Coleochsete) the thallus (Fig. 314),is in the form of a flat disk or mass attachedto some support by the lower surface. This disk as in thespecies figured usually of branching filaments whichelongate by repeated division of the terminal cell and branchby its frequent forkings. (B,a-g). In other .species the fila- Fla-gel
. Plants and their uses; an introduction to botany . oming a resistant zygosporeready for a period of rest. The zygospore germinates b\- formingseveral swarm-spores (A) each of which in turn grows into a thallusas already described. In the sheath algae (Coleochsete) the thallus (Fig. 314),is in the form of a flat disk or mass attachedto some support by the lower surface. This disk as in thespecies figured usually of branching filaments whichelongate by repeated division of the terminal cell and branchby its frequent forkings. (B,a-g). In other .species the fila- Fla-gellum < L. a whip. * Zygotc < Gr. , yoked. THE GREEN 483 ments instead of being distinct grow togetlier into a massby the coalescence of adjacent cells. Many of the cellsproduce hair-hke outgro^i;hs, and they are all uninucleate. Any of the cells may form a single swarm-spore like that shownin Fig. 315 Z), which, as will be noticed, has but two flagella. Such aspore, after attacliing itself to some support, divides iuto a cell-row. Fig. 314.—Free-branching Sheath-alga {Coleochoete soluta. Sheath-algaFamily, Coleochcetaceae). A, plant showing flat system of branching,and bristle-like outgrowths (h), ip. B, part of disk, further enlarged;a-g show successive stages in the branching of terminal cells. (Pring-sheim.)—Thallus forming bright green spots on plants or other sub-merged objects in fresh water, in Europe and America. which bj^ further di\-ision becomes a mature thallus. Besides thisnon-sexual method of propagation a well-marked sexual reproduc-tion takes place as follows. The protoplasts of certain small usualhterminal cells (an, Fig. ., A) become transformed into flagellatebodies like the swarm-spores only smaller (z); while other terminalcells (og, Fig. 315, A) enlarge, become flask-shaped by the formatiocof a long neck opening at the top, and finally contract the protoplastinto a sphere at the base. The motile body as soon as it is set freeswim
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1913
