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Plants--Effect of acids on; Isoetaceae; Plant morphology; Shoot apexes


Isoetes macrospora Dur. was found growing in 20 inches to 4 ft. of water in several sandy-bottomed lakes in Itasca County, Minnesota. The pH of the lakes was about 6 and the characteristic tree species of the immediate shorelines were: Thuja occidentalis, Pinus resinosa, Abies balsomea, Populus tremuloides, and Betula papyrifera. Experimental and normal plants were grown submerged in 1-liler beakers in the greenhouse for the 2-week experimental period. The normal shoot apex of /. macrospora is described as having three zones. Zone I, the metrameristem, consists of the superficial layer of initials which divide usually by anticlinal divisions and sometimes periclinal divisions, and the underlying region of irregularly dividing initials. Laterally the metrameristem contributes to zone II, the flanking meristem which gives rise to leaf primordia and primary cortical tissue. Underlying the metrameristem is zone Ill, the central rib meristem which is responsible for growth in length of the plant axis, and is distinguishable from the flanking meristem by position and orientation of cell files. Apical dome height and zonation is similar to that of other species of Isoetes. Experimental plants were treated l and 2 weeks with 10 ppm, 30 ppm, and 70 ppm IAA; 10 ppm, 30 ppm, and 70 ppm GA; and several plants sprayed with a 90 ppm water solution of GA. A proliferation of cortical tissue in the upper port of the corm resulted in plants treated 2 weeks with 30 ppm and 70 ppm IAA. The other treatments produced no obvious results.

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