Plants and their ways in South Africa . greenhouses. Several species are native to South Africa. Atthe tips of the branchessporangia are clustered toform a cone. In some spor-angia only one of the manyspore mother-cells develops,so that when ripe they con-tain only four large sporeseach (megaspores). Those inwhich all the spore mother-cells develop contain a largenumber of small spores (mi-crospores). The megasporesgerminate within the spor-angium each forming a pro-thallium much more reducedthan that of the fern, in factthe cells barely emerge fromthe ruptured spore wall,where a few archegoni
Plants and their ways in South Africa . greenhouses. Several species are native to South Africa. Atthe tips of the branchessporangia are clustered toform a cone. In some spor-angia only one of the manyspore mother-cells develops,so that when ripe they con-tain only four large sporeseach (megaspores). Those inwhich all the spore mother-cells develop contain a largenumber of small spores (mi-crospores). The megasporesgerminate within the spor-angium each forming a pro-thallium much more reducedthan that of the fern, in factthe cells barely emerge fromthe ruptured spore wall,where a few archegonia areformed. The prothallium formed from the microspore is stillmore reduced and consists of a smgle cell. But one anther-idium is formed which produces several sperm-cells. After fertilization, an embryo is developed from the egg-cell which for a time derives its nourishment from the smallprothallium. Later, like the fern, it forms roots and becomesan independent plant. The life history of the fern may be shown by the diagrambelow:—. Fig. 208.—Longitudinal section througha cone of Selaginella. a, macrospor-angium ; d, microsporangium. Classification of Plants n% Prothallium t Spores t , C/3 Sporangium o t XT Fern Plant ^ t Oospore t t o Sperm cell Egg cell p .t t itheridium Archegonium o ^3 t t Prothallium J? Spermaphyta or Seed-Bearing Plants. Although seed formation was given as a distinguishingcharacter of Spermaphyta, the nucellus of the ovule may becompared to the megasporangium of Selaginella^ where how-
Size: 1326px × 1884px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectplants, bookyear1915
