. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. REPRODUCTION OF EOUISETUM 313 and bears on the inner face of its hexagonal lamina a ring of 5 to 10 sporangia encircling the stalk (Fig. 176, B). In the }'oung cone the heads of the sporopln'lls fit closely together, thus forming a compact protection for the sporangia; lint as the latter mature the sporoph5'lls separate, through elongation of the axis, and permit escape of the green spores. The individual sporangia are rather larger than those of Ferns, and have a several-layered wall. Many of the fossil Hors
. An introduction to the structure and reproduction of plants. Plant anatomy; Plants. REPRODUCTION OF EOUISETUM 313 and bears on the inner face of its hexagonal lamina a ring of 5 to 10 sporangia encircling the stalk (Fig. 176, B). In the }'oung cone the heads of the sporopln'lls fit closely together, thus forming a compact protection for the sporangia; lint as the latter mature the sporoph5'lls separate, through elongation of the axis, and permit escape of the green spores. The individual sporangia are rather larger than those of Ferns, and have a several-layered wall. Many of the fossil Horsetails possessed cones of more elaborate structure. At maturity the outermost coat of each spore is seen to consist of four extremely hygro- scopic spiral strips (Fig. 176, C, D) which only remain attached at one point. Groups of spores consequentl}' tend to cling together when the contents of a sporangium are scattered by the wind, and this may be of importance, since the archegonia and anthe- ridia are usually pro- duced on distinct prothaUi. The spores are, however, all alike, the sex of the resulting prothaUi depending on the conditions of nutrition, those poorl}' nourished becoming male, '\\hilst those well nourished become female. Both kinds are more or less richl)' branched, but the male are smaller than the female. The sexual organs borne upon them do not differ essentiallj^ in construction from those of Ferns. It may be noted that, when Fern prothaUi grow densely crowded, they often bear antheridia only, although unisexuality is here the exception rather than the rule. The present-da}' Clubmosses are represented mainly bj- the. Fig >.—A, Entire cone, and B, single sporophyll of Eqiiiseliim maximinn (ori- ginal). C and D, Mature spores, showing the splitting of the outer coat (C after Sachs; D after Dodel-I' Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appeara
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpl, booksubjectplants
