. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. SECONDARY THICKENING. NORMAL DICOTYLEDONS. 493 canals often arise in them'; in the wood of Prunus avium, they are, according to Wigand ^, a principal starting-point of the disorganisation which produces the cherry- gum. The dilatations of the medullary rays and the medullary spots occur, it is true, relatively seldom ; they are, however, characteristic of many woods, both Dicotyledonous and Coniferous. Ac- cording to Kraus and Nordlinger they have been frequently observed in Betula alba, dahuric
. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. SECONDARY THICKENING. NORMAL DICOTYLEDONS. 493 canals often arise in them'; in the wood of Prunus avium, they are, according to Wigand ^, a principal starting-point of the disorganisation which produces the cherry- gum. The dilatations of the medullary rays and the medullary spots occur, it is true, relatively seldom ; they are, however, characteristic of many woods, both Dicotyledonous and Coniferous. Ac- cording to Kraus and Nordlinger they have been frequently observed in Betula alba, dahurica, populifolia, Crataegus oxyacantha, monogyna, pyracantha, cor- data, Cydonia vulgaris, Pyrus prunifolia, Amygdalus communis, Cotoneaster mi- crophylla, Prunus spinosa, Salix aurita, Caprea, bicolor, Rhus Cotinus, Lilhea grandifolia, Pterocarya caucasica, Vac- cinium Myrtillus, Vitex incisa, Calluna vulgaris, Erythroxylon grandifolium, Guazuma ulmifolia, and Liquidambar styraciflua, besides the plants mentioned above ; while they occur rarely in Alnus viridis, Catalpa, Magnolia acuminata, and Salix triandra. I leave unmentioned the cases marked (?) by Nordlinger. Among the Coniferous woods Kraus found them in Abies balsamea, Pindrow, Pichta, Picea orientalis, and Juniperus excelsa; in Abies pectinata, Cedrus Deo- dara and Larix, he only found swellings of the medullary rays. In Dicotyle- donous woods the passages occur chiefly in the lower part of the stem, and are thence continued into the roots; they also extend, however, into the apices and branches, though here they are less numerous and constant. In the Coni- ferous woods their course has not been minutely investigated ; according to Dippel's statements (/. c), which concern this particular point but little, those in the white Fir which contain resin canals may be traced longitudinally for considerable' Fig. 208,—Pintis silvestris; radial longitudinal section through the wood of a branch, a—e ends of trach
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Keywords: ., bookcentury1800, bookdecad, booksubjectplantanatomy, bookyear1884
