. A manual of botany. Botany. 62 MANUAL OF BOTANY Coleochcete is a form whioh in some respects approaches the red seaweeds. Its thallus is composed of much-branched filaments forming a tufted mass which grows apically or mar- ginally. The cells in some cases bear peculiar sheathing hairs. The plant bears antheridia and oogonia, each of the latter bearing a trichogyne except in a few species. The antherozoid enters the oogonium by an opening in the trichogyne and fertilises the oosphere. The result of the fusion is the production of a more elabo- rate sporophyte than in any other member of the
. A manual of botany. Botany. 62 MANUAL OF BOTANY Coleochcete is a form whioh in some respects approaches the red seaweeds. Its thallus is composed of much-branched filaments forming a tufted mass which grows apically or mar- ginally. The cells in some cases bear peculiar sheathing hairs. The plant bears antheridia and oogonia, each of the latter bearing a trichogyne except in a few species. The antherozoid enters the oogonium by an opening in the trichogyne and fertilises the oosphere. The result of the fusion is the production of a more elabo- rate sporophyte than in any other member of the Chloro- phyceie. The oosphere se- FiG. 810. cretes a cell-wall round it, and the oogonium in which it lies becomes surrounded by a kind of cellular covering derived from the cells of the thallus near it. It thus forms a kind of fructification which becomes detached from the parent. Later the oospore germinates, â rupturing its coating ; it only produces a few cells, each of which gives rise to a single zoospore. The asexual reproductive cells produced by the Confer- voidese are zoogonidia or zoo- spores, as they are, produced on the gametophyte or the sporophyte respectively. They are variously ciliated, and always on germination pro- duce a gametophyte {fig. 809). The process of asexual reproduction is not found in the Desmids nor in the Zygnemise. The last type of structure is found in the ChaeacEjE, repre- sented most familiarly by the two genera Chara and Nitella. In some respects these approach nearest in structure to the Bryophytes ; among the ChlorophyceEe they are distinguished by their relatively great degree of both morphological and anatomical differentiation and by the complex structure of their reproductive organs. Chara exhibits a long slender stem, bearing whorls of leaves. Fig. 810. Longitudinal section through the apical region of tluree primary shoots of Charafragilis. t. Apical cell, in wliicli segments are formed by septa, each segment being further divided
Size: 1525px × 1638px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
