. The structure and development of mosses and ferns (Archegoniatae). asily demonstrated. According to Janczewski (4) these pitsdo not penetrate the membrane between the cells, but Russows(5) assumption that there is direct communication between thecells is correct, although difficult to prove. Russow also statesthat callus is present in the sieve-plates of Botrychmm, althoughpoorly developed. According to Janczewski the pores are notconfined to the transverse walls, but may also occur, but muchless frequently, in the longitudinal walls. The contents of the 266 MOSSES AND FERNS CHAP. sieve-tube
. The structure and development of mosses and ferns (Archegoniatae). asily demonstrated. According to Janczewski (4) these pitsdo not penetrate the membrane between the cells, but Russows(5) assumption that there is direct communication between thecells is correct, although difficult to prove. Russow also statesthat callus is present in the sieve-plates of Botrychmm, althoughpoorly developed. According to Janczewski the pores are notconfined to the transverse walls, but may also occur, but muchless frequently, in the longitudinal walls. The contents of the 266 MOSSES AND FERNS CHAP. sieve-tubes consist of a thin parietal layer of protoplasm inwhich numerous nuclei are imbedded. Little glistening glob-ules are also found, especially close to the openings of the poresof the sieve-plates. The lamina of the sterile segment of the leaf is composedof a spongy green mesophyll, more compact on the upper sur-face. The epidermal cells show the wavy outlines characteristicof the broad leaves of other Ferns, and develop stomata onlyupon the lower side of the Fig. 146.—Botrychium Virginianum. A, Longitudinal; B, transverse sections of the root apex, X200; pi, plerome. The Root The roots arise singly at the bases of the leaves, and inolder plants branch monopodially. Like those of Ophioglossumthey have no root-hairs, but the smooth surface of the youngerroots becomes often strongly wrinkled in the older ones. Sec-tions either transverse or longitudinal, through the root tip,when compared with those of Ophioglossum, show a very muchgreater regularity in the disposition of the cells. This is lessmarked in B. ternatum, and probably an examination of suchforms as B. simplex will show an approximation to the condi-tion found in Ophioglossum, although Holles figure of B. luna^ VII PTERIDOPHYTA—FILICINEJE—OPHIOGLOSSACEAi 267 ria shows even greater regularity in the arrangement of theapical meristem than is found in B. I iri^ijiicniiiin. A carefulexamination of this point is
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