Nature and development of plants . OF ULOTHRIX able. When new conditons arise, such as changes of tempera-ture, food, etc., that would interfere with the normal growth ofthe individuals then a modification of the contents of the cellsand its mode of division results. The cells of Ulothrix as a con-sequence of such alterations divide into larger numbers of motilebodies which are consequently smaller than in the case of zoo-spores (Fig. 112, A). These bodies may behave as gametes andunite, forming gametospores. The cells in which gametes areformed are called gametangia, sing, gametangium. Thus,
Nature and development of plants . OF ULOTHRIX able. When new conditons arise, such as changes of tempera-ture, food, etc., that would interfere with the normal growth ofthe individuals then a modification of the contents of the cellsand its mode of division results. The cells of Ulothrix as a con-sequence of such alterations divide into larger numbers of motilebodies which are consequently smaller than in the case of zoo-spores (Fig. 112, A). These bodies may behave as gametes andunite, forming gametospores. The cells in which gametes areformed are called gametangia, sing, gametangium. Thus, Ulo-tlirix is controlled in the same manner as Chlamydomonas andHydrodyction. It is interesting to note, however, that thesesmall bodies frequently behave as zoospores and develop intosmall and weak plants, which fact accounts for the common asso-ciation in this genus of puny and vigorous plants (Fig. ill,C,E). These small bodies of Ulothrix represent a curious intermediatecondition between a zoospore and a gamete where the sexual. Fig. 112. Sexual reproduction of Ulothrix: A, a few cells of a filamentshowing the formation and escape of the gametes. B, gamete. C, D,stages in the union of the gametes. E, gametospore. F, gametosporegerminating and forming a single-celled plant in which several zoosporesarc developing. character is not strongly enough developed to overcome com-pletely the zoospore character. Thus, we sec again in Ulothrix DEVELOPMENT OF PLANTS 173 that definite environmental conditions caused motile bodies to beproduced that are lacking in some essential substance and conse-quently do not have the energy for growth, or at least can onlydevelop into feeble plants. This weakness is overcome by thefusion of two gametes which results in the formation of a cellor gametospore with renewed energy for growth. The gametospore germinates after the period of rest in a rad-ically different manner from previous cases. The contents ofthe spore, instead of giving rise directly t
Size: 1363px × 1833px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublisher, booksubjectplants
