. A textbook of botany for colleges and universities ... Botany. 792 ECOLOGY outside), while if the fungi occur within the roots, as in the orchids (fig. 1106), it is called endotrophic { nourished within). Ecto trophic mycorhizas vary from forms with loose and scattered hyphal threads which come into casual contact with the roots to a condition like that in Monoiropa, where the root system usually is compacted into a clump or ball, and where the in- dividual rootlets are so closely invested by fun- gal hyphaethatthelatter when sectioned resem- ble a compact tissue (figs. 1104, 1105); in s
. A textbook of botany for colleges and universities ... Botany. 792 ECOLOGY outside), while if the fungi occur within the roots, as in the orchids (fig. 1106), it is called endotrophic { nourished within). Ecto trophic mycorhizas vary from forms with loose and scattered hyphal threads which come into casual contact with the roots to a condition like that in Monoiropa, where the root system usually is compacted into a clump or ball, and where the in- dividual rootlets are so closely invested by fun- gal hyphaethatthelatter when sectioned resem- ble a compact tissue (figs. 1104, 1105); in such a case the root proper does not come into contact with the soil. The hyphae com- posing the fungal root sheath connect with the mycelia that permeate the humus. The root- lets of the beech and of most plants with prominent ectotrophic mycorhizas are rela- tively short and thick and have a coralloid aspect; moreover, growth is relatively sluggish and root hairs are few or wanting except on roots or on parts of roots that are comparatively free from fungi. Endotrophic mycorhizas, which especially characterize the orchids, are in many respects much more specialized than are the ectotrophic forms. Orchid roots are characteristically fleshy and tuber-like, differ- ing much more from ordinary roots than do those associated with ecto- trophic fungi; furthermore, the endophytic fungi appear to be specialized forms rather than ordinary soil fungi. Certain cortical cells contain closely interwoven clumps of hyphae which commonly enfold the nucleus, and there are hyphal connections with similar clumps in adjoining cells,. Figs. 1104, 1105. — Mycorhiza of the Indian pipe {Monotropa uniflora): 1104, the basal portion of a. stem with its dump of roots; note the coralloid root system (r), and the imbricated scale leaves (s); 1105, a cross section through the outer part of one of the coralloid roots, showing the compact arrangement of the fungal hyphae which iorm a pseudo-parenchyma (/);
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
