. Botany, an elementary text for schools. Botany. ALTEEXATIOX OF GENETIATTOXS 195 The fungi and algte are omitted from tliese remarks. In the former tliere is nothing analogous to the sporophyte and the gameto- phyte. In algfe like spirogyra, evidently the whole plant is a ga- metophyte and, since the zygospore germinates directly into a new gametophyte, there is probably no sporophyte. In some other algje traces of a sporophyte have been found, but the discussion of these would lead too far for the present purpose. In the ferns the egg-cells are developed on the j^rothallus. This then is the
. Botany, an elementary text for schools. Botany. ALTEEXATIOX OF GENETIATTOXS 195 The fungi and algte are omitted from tliese remarks. In the former tliere is nothing analogous to the sporophyte and the gameto- phyte. In algfe like spirogyra, evidently the whole plant is a ga- metophyte and, since the zygospore germinates directly into a new gametophyte, there is probably no sporophyte. In some other algje traces of a sporophyte have been found, but the discussion of these would lead too far for the present purpose. In the ferns the egg-cells are developed on the j^rothallus. This then is the gametophyte. It corresponds to the thallus of mar- chantia and to the ''moss plant," but it has become much reduced. The plant developing from the fertilized egg-cell is the large and beautiful "fern plant" differentiated into stems and leaves. Since the fern plant produces the spores directly, it is the sporophyte and eon-esponds to the shaft and capsule of the mosses. Both sporophyte and gametophyte lead an independent existence. As we pass on to equisetura and isoetes, the sporophyte is still moi-e conspicuous in comparison with the gametophyte. In isoetes the prothaUus (gametophyte) is very rudimentary, consisting only of a few cells remaining within the spore, which merely bursts to expose the archegonia or to allow the sperm-cells to escape. Moreover, the spores have become differentiated into micro- and macrospores corre- sponding to the pollen and embryo-sac of higher plants. This gradual increase of the sporophyte and reduction of tlie gametophyte can be traced on through the flowering plants in which "the plant" is the sporophyte, and the gametophyte is rrpitscntcd simply by a few cells in the gi-i'miiiating j)nlU-n grain, and in the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble
Size: 1898px × 1317px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorbai, bookcentury1900, bookdecade1900, booksubjectbotany
