. The structure and development of mosses and ferns (Archegoniatae). s : Tn Marattia the first differentiation of the spo-rangium begins while the young leaf is still rolled up between thestipules of the next older one. The tissue above the fertile veinis more strongly developed than the adjoining parenchyma, andforms an elevated cushion parallel with the vein. This is thereceptacle, which develops two parallel ridges, separated by acleft. These two ridges grow up until they meet, and theiredges grow together and completely close the cleft which lies VIII MARATTIALES 293 between. In each half
. The structure and development of mosses and ferns (Archegoniatae). s : Tn Marattia the first differentiation of the spo-rangium begins while the young leaf is still rolled up between thestipules of the next older one. The tissue above the fertile veinis more strongly developed than the adjoining parenchyma, andforms an elevated cushion parallel with the vein. This is thereceptacle, which develops two parallel ridges, separated by acleft. These two ridges grow up until they meet, and theiredges grow together and completely close the cleft which lies VIII MARATTIALES 293 between. In each half there are differentiated the separatearchesporial groups of cells corresponding to the separatechambers found in the complete synangium. The wholeprocess takes, according to his account, about six was unable either in Marattia or Augioptcris to traceback the archesporium to a single cell, which Goebel (3) claimsis present in the latter. In Angioptcris the process begins as in Marattia, but at aperiod when the leaf is almost completely developed and. Fig. 164.—Angiopteris evecta. Development of the sporangium. A, Vertical sectionof very young receptacle; B, similar section of an older sporangium in which thearchesporium is already developed (after Goebel); C, longitudinal section of analmost fully-developed sporangium, showing the persistent tapetal cells (0 ; r, theannulus, X75 unfolded. The first indication of the young sorus is theformation of an oblong depression above a young vein, andabout the border of this are numerous short hairs, which as arule are absent from the epidermis of the leaf (Fig. 164, A).The placenta is formed as in Marattia, but instead of the twoparallel ridges that are found in the latter, the young sporangiaarise separately, much as in Botrychmm. As in the latter too,Goebel states that the archesporium can be traced to a single 294 MOSSES AND FERNS CHAP. hypodermal cell in the axis of the young sporangium. Thiscell divides repeatedly,
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
