. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . fore never form a connected net-like thallus such as occurs sofrequently in the Valoniacese. On the germination of the zoogonidium or of the zygote there is from thevery first a differentiation of the thallus into a cauloid part and a rhizoid latter usually consists of a few basal segments, but it may consist of astrong hold-fast resulting from the growing together of a number of rhizoidalfilaments, as in Cladophora rupestris. Other
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . fore never form a connected net-like thallus such as occurs sofrequently in the Valoniacese. On the germination of the zoogonidium or of the zygote there is from thevery first a differentiation of the thallus into a cauloid part and a rhizoid latter usually consists of a few basal segments, but it may consist of astrong hold-fast resulting from the growing together of a number of rhizoidalfilaments, as in Cladophora rupestris. Other rhizoids, which are developedfrom the cauloid part of the thallus, may be described as accessory rhizoids. Cladophorese 261 These are sometimes intracuticular, arising from segments high up on theaxis and passing down between the lamellae of the cell-wall, finally breakingthrough to the exterior in the lowermost part of the thallus (Brand, 09)This type of rhizoid is more particularly characteristic of Spongomorpha inthe Rhizoclonieoe. In Cladophora glomerata var. callicoma there are oftenstoloniferous branches from which new erect shoots arise. ou. Fig. 167. A and B, Cladopliora, incurvata W. & G. S. West, a Cingalese species which showspolytomous branching very well; A, x 2^; B, x54. C—E, successive stages in theformation of a transverse wall in Cl. glomerata (L.) Kiitz., x 900 (after Brand). F, oldercondition of same showing the joint (j), x 675. i, inner layer of cell-wall; o, outer layer;ou, outermost layer. The segments of the thallus are very variable in length, being usuallyfrom 6 to 12 (or even 20) times as long as their diameter. In Cladophorafuliginosa Kiitz. very long segments occur, sometimes (as noticed by bothHarvey and Borgesen) a whole branch being without a transverse wall. Thecell-wall consists of an inner and an outer layer, both of which are lamellose, 262 Sip/i onocladiales
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