. Plants and their uses; an introduction to botany . part of astalk 2 cm. in diameter, »,, showing the darker rind (r, r) containingslime-canals (g, g); and the lighter interior tissue (p, p) which form thegreater l)ulk. (Luerssen.) Fig. 318.—Hladdcr-wrack {Fucus vesiculosus. Wrack Family, Fucacece).Branch bearing air-bladders (/) and swollen tips (s) containing con-ccptades. (Luerssen.)—Brown, slimy, tough seaweed, sometimes 1 , growing attached to rocks, etc., between tides along the NorthAtlantic coast. A comparatively simple type is the thread-weed (Nemalion,Fig. 320). The thallus is
. Plants and their uses; an introduction to botany . part of astalk 2 cm. in diameter, »,, showing the darker rind (r, r) containingslime-canals (g, g); and the lighter interior tissue (p, p) which form thegreater l)ulk. (Luerssen.) Fig. 318.—Hladdcr-wrack {Fucus vesiculosus. Wrack Family, Fucacece).Branch bearing air-bladders (/) and swollen tips (s) containing con-ccptades. (Luerssen.)—Brown, slimy, tough seaweed, sometimes 1 , growing attached to rocks, etc., between tides along the NorthAtlantic coast. A comparatively simple type is the thread-weed (Nemalion,Fig. 320). The thallus is .small and with slender branches whichgrow at the apex Init do not show much differentiation among thevegetative cells. Male gametangia (/, ^p) are developed at the tips THE RED ALGiE 489 of certain branches, and these emit minute, spherical gameteshaving no flagella or other means of locomotion. At the tips ofother branches female gametes appear, each in the form of a flask-shaped ceU with long, slender neck (/, 0- Fertilization is effected. Fig. 319.—Bladder-wrack; a, vertical section through a conceptacle {^f)showing the female gametangia; h, female gametangium beginning toform its eight gametes; c, the same, beginning to set free its gametes;d, male gametangia (shaded) from which come ciliatc gametes like theone (fif) shown near by; e, female gamete surrounded by numerous malegametes which cause it to revolve in the water; /, young plant produceddirectly from the fertilized female gamete, h-f, ^\^, g, -ifa. (Thuret.) by fusion of male gametes with the projecting end of a female gameteto which the little spheres have been brought by currents in thewater. After fertilization the basal part (/-F, c) gives rise to severalbranches, each of which finally produces at its tip a spheroidal sporethat soon separates, and attaching itself to some support, developes 490 LIFE-HISTORIES into a new Xemalion plant. Spores wliich are thus the indirectproduct of fertilization are call
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1913
