. Fundamentals of botany. Botany. 374 STRUCTURE AND LIFE HISTORIES isolation of single spores is prevented, and the advantage of this is recognized at once when we recall that the prothallia are dioecious. 335. The Gainetoph3^es.—Under suitable conditions of moisture and temperature the spores begin to germinate, and by successive cell-divisions produce the lobed pro- thallia. The male prothallia are one cell in thickness, and bear the antheridia at the tips of the lobes or on the margins (Fig. 269).. Fig. 270.—Female prothallus of Equisetum arvense L. ari, young archegonium; ar2, archegoium b
. Fundamentals of botany. Botany. 374 STRUCTURE AND LIFE HISTORIES isolation of single spores is prevented, and the advantage of this is recognized at once when we recall that the prothallia are dioecious. 335. The Gainetoph3^es.—Under suitable conditions of moisture and temperature the spores begin to germinate, and by successive cell-divisions produce the lobed pro- thallia. The male prothallia are one cell in thickness, and bear the antheridia at the tips of the lobes or on the margins (Fig. 269).. Fig. 270.—Female prothallus of Equisetum arvense L. ari, young archegonium; ar2, archegoium before fertilization; st, sterile lobe of pro- thallus; hw, rhizoids. Several lobes were removed in order to show the cushion and the archegonia. Enlarged about 20 times. (After Sadebeck.) The female prothallia form a cushion of relatively thick, spongy tissue (the meristem), and on this cushion (as in all Pteridophytes) are borne the archegonia. In contrast to the true ferns, the archegonia are borne on the upper surface of the prothallus, and point upward, in consequence of being negatively geotropic (Fig. 270). From the edges of the cushion numerous thin flaps of green tissue form; these fold over the cushion, enclosing the archegonia, and thus retaining the moisture of dew. 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 the original Gager, C. Stuart (Charles Stuart), 1872-1943. Philadelphia, P. Blakiston's son & co.
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