. Botany for high schools and colleges. Botany. 80 BOTANY. regarded as undeveloped sieve ducts, and lience the tissue they form may be included under sieve tissue. Latticed cells are thin-walled and elongated ; they differ from true sieve ducts principally in being of less diameter, and in having the markings but not the perforations of sieve discs. Both of these differences are such as might be looked for in un- developed sieve tissue. 106.âIn the corres- ponding parts of the vas- cular bundles of Gymno- sperms and Pterido- phytes a sieve tissue is found which differs somewhat from that in An
. Botany for high schools and colleges. Botany. 80 BOTANY. regarded as undeveloped sieve ducts, and lience the tissue they form may be included under sieve tissue. Latticed cells are thin-walled and elongated ; they differ from true sieve ducts principally in being of less diameter, and in having the markings but not the perforations of sieve discs. Both of these differences are such as might be looked for in un- developed sieve tissue. 106.âIn the corres- ponding parts of the vas- cular bundles of Gymno- sperms and Pterido- phytes a sieve tissue is found which differs somewhat from that in Angiosperms. In Gym- nosperms the sieve discs, which are of irregular outline, occur abundant- ly upon the oblique ends and radial faces of the Longitudinal broad tubes (Fig. 70). ^^^g^tirof The^gVp^e! In Pteridophytes the SrfSf?"^ve"'&^^ tubes have varying ^i?i?a^s,?bsfaL''cl'''*«!}rifoâ¢s; in Equisetum After DeBary. g^XlA OpMogloSSUm they are prismatic, with numerous horizontal but not vertical sieve discs ; \ti Pteris and many other ferns they have pointed extremities, and are greatly elongated, bearing the sieve discs upon their sides (Pig. 71). In the larger Lyaipodiacem the sieve tubes are pris- matic and of great length; in the smaller Srsfem^YhVive species there are tissue elements destitute of P'*Jf^ ^''^'''i^^i?,'' ^ erally ana are com- sieve discs, but which are otherwise, includ- posed of many little ,, , ,, ,-, ,, punctured areas mar position m the stem, exactly like the grouped togethenr- .^ ^ , â ,, 1 . â ' regularly, x 375- sieve ducts of the larger species. After De Bary. (a) Good specimens of sieve tissue may be obtained for study by making; longitudiual sections of tlxe stems of Oucurbita, Cucvmii,. Fig. 70. â Radial view of the end of a sieve tube of Segu'da taken. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations m
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1885
