Nature and development of plants . : ./, Closterium. B, , Xanthidium. D, Straustrastrum. At left top view, at right side , Desmidium forming a chain of plants. At righl end view of chain. DEVELOPMENT OF PLANTS 169 The Desmids.—A second group of the Zygnematales arestrictly unicellular plants known as Desmids (Fig. 108). Theyare the most attractive of unicellular plants and are of commonoccurrence associated with coarse algae. The desmids are elabo-rately and variously fashioned but can readily be recognized bythe fact that they consist of two similar halves (Fig. 109, A).Th
Nature and development of plants . : ./, Closterium. B, , Xanthidium. D, Straustrastrum. At left top view, at right side , Desmidium forming a chain of plants. At righl end view of chain. DEVELOPMENT OF PLANTS 169 The Desmids.—A second group of the Zygnematales arestrictly unicellular plants known as Desmids (Fig. 108). Theyare the most attractive of unicellular plants and are of commonoccurrence associated with coarse algae. The desmids are elabo-rately and variously fashioned but can readily be recognized bythe fact that they consist of two similar halves (Fig. 109, A).The structure of the cells and the sexual method of reproductionis essentially the same as in the filamentous forms which haveprobably been derived from these unicellular plants. The asex-ual method of reproduction, however, is rather peculiar. Theregion connecting the two halves (Fig. 109, A, i), called the isth-mus, becomes somewhat elongated and swollen. Soon a con-striction appears midway between these two halves which deepens. Fig. log. Reproduction of Cosmarium: A, asexual reproduction, show-ing the elongation of the isthmus, i, and its gradual enlargement and divi-sion to form the new lobes of the desmids. B, sexual reproduction. Atthe left the cell contents of two desmids fusing to form a the right the mature gametospore covered with a spiny coat. until the desmid is cut in half. Each desmid now consists of oneof the original halves and one half of the isthmus. This latterpart gradually enlarges and forms the second half of the to the gelatinous character of the cell walls, the desmids i/o DEVELOPMENT OE ULOTHRIX often become aggregated in masses and form chains of cells(Fig. 108, £). 69. Order c. Chaetophorales or Filamentous Green Algae.—Here belong a great array of green algae that grow attached tovarious objects and appear as simple or more usually as branchedfilaments which frequently end in hair-like tips. They are ofcommon occurrenc
Size: 1733px × 1442px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisher, booksubjectplants
