. The structure and development of mosses and ferns (Archegoniatae). s has been frequently asserted, Fig. . natans. A, but rather proteraudrous—that is,Floating form; B, terrestrial numcrous antheridia are formed,form, X2. ^^^ some time before the first arch- egonia develop. Occasionally no archegonia are formed. While the settling of the plant upon the mud is not a neces-sary condition for the development of the reproductive organs,as has been asserted by Leitgeb, still none are formed as a ruleupon plants growing in permanent ponds, while those growingin temporary ponds regula
. The structure and development of mosses and ferns (Archegoniatae). s has been frequently asserted, Fig. . natans. A, but rather proteraudrous—that is,Floating form; B, terrestrial numcrous antheridia are formed,form, X2. ^^^ some time before the first arch- egonia develop. Occasionally no archegonia are formed. While the settling of the plant upon the mud is not a neces-sary condition for the development of the reproductive organs,as has been asserted by Leitgeb, still none are formed as a ruleupon plants growing in permanent ponds, while those growingin temporary ponds regularly develop abundant reproductiveorgans. In permanent bodies of water, vegetative multipli-cation may be very rapid, and it has been found that after theseare frozen over, a certain number of the plants survive, some-times sinking to the bottom, and resuming growth again inthe spring. The third genus, Tesselina (Oxymifra), represented by thesingle species, T. pyramidata, is much less widely distributed,belonging mainly to Southern Europe, but also found in Para-. 11 MUSCINEJE—HEPATIC JE—MARCH ANTI ALES 41 guay. This interesting form has also been carefully examinedby Leitgeb ((7), iv., p. 34), who calls attention to its inter-mediate position between the RicciacCcC and the thallus has all the characters of the latter: air-chambersopening by regular pores, usually surrounded by six guard-cells ; two rows of ventral scales, independent from the begin-ning; and the sexual organs united into groups upon specialparts of the thallus. The sporogonium, how^ever, is entirelylike that of Riccia, so that it may properly be placed in the samefamily. The plants are dicecious and strictly terrestrial. A third genus, Croiiisia, represented also by a single species,C paradoxa, is placed provisionally with the RicciacCcC bySchififner ((i), p. 15), but the structure and development havenot been investigated with sufficient completeness to make thiscertain. It has been fo
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