. The structure and development of mosses and ferns (Archegoniatae). Fig. 149.—Angiopteris evecta. Germination of the spores,—A, B, X220; C, X175;sp, spore membrane; x, apical cell (after Jonkman), the apical cell, and this is followed by a longitudinal wall in theouter one, forming two similar cells wdiich, by further longi-tudinal divisions, may produce a row of marginal initials, andthe subsequent growth of the prothallium is due to the divisionsand growth of this group of initial cells (Fig. 150, A). At first the prothallium has a spatulate form, but before thesingle apical cell is replace
. The structure and development of mosses and ferns (Archegoniatae). Fig. 149.—Angiopteris evecta. Germination of the spores,—A, B, X220; C, X175;sp, spore membrane; x, apical cell (after Jonkman), the apical cell, and this is followed by a longitudinal wall in theouter one, forming two similar cells wdiich, by further longi-tudinal divisions, may produce a row of marginal initials, andthe subsequent growth of the prothallium is due to the divisionsand growth of this group of initial cells (Fig. 150, A). At first the prothallium has a spatulate form, but before thesingle apical cell is replaced by the group of marginal initials,the outer cells of the segments grow more rapidly than theinner ones, and the segments project beyond the apical cell, 276 MOSSES AND FERNS which comes to lie in a depression between the two lobes formedby the outer parts of the segments, and the prothallium assumesthe heart-shape found in most homosporous Ferns. The sec-ondary initial cells vary in number with the width of the inden-tation in which they lie. Seen from the surface they are oblongin shape, but in vertical section are nearly semicircular (, B). Basal segments are cut off by a wall that extendsthe whole depth of the prothallium, and the segment is thendivided by a horizontal wall into a dorsal and ventral cell ofnearly equal size. The divisions are more numerous in the ventral than in the dorsalcells of the segment, thisdifference first being mani-fest some distance back ofthe apex. Owing to this, astrongly projecting, nearlyhemispherical cushion - likemass of tissue is formedupon the ventral superficial cells of bothsides of the prothallium havea well-marked cuticle. Nu-merous brown rhizoids,which, like those of the sim-pler Liverworts, a
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
