® ° are = s 
Observations on the Vascular System of Ferns. 115 
with wrth ease when the plant is young, but with more difficulty 
in the adult plant. The uncoiled- duct, when examined by 
magnifying power, has. all the appearance of a common 
vessel; but when highly magnified, it shows. the real structure 
to be as represented in Fig. 4, Plate I. It will be seen, that this 
differs ° very much from the structure of a true spiral vessel, which, 
shows merely one or more continuous, slender, round fibres, en- 
tirely destitute of any marks; while the uncoiled ducts of ferns 
show, as in the figure, a flat ribbon marked with peeie rows of 
Short ae 
To oben these = separate from each other, go. as to allow 
the state in which they exist in the plants to be seen, 1 macera- 
ted in water for several weeks the bundles of weasels from the 
petioles of young and tender, though large fronds of Onoclea 
sensibilis, Osmunda cinnamomea, &c. until by the decay of the 
connecting parts, the vessels could be easily separated from each 
other by placing a portion on glass, in a drop of water, and fore- 
ing them apart with the points of fine needles. ~The vessels, as 
prepared in this manner, present the appearance of long cylindri- 
cal (Fig. 2, Plate I,) or prismatic (Fig. 3, Plate I,) tubes, termi- 
nating at each end in very elongated cones. These tubes vary 
much in length and diameter, some being several inches long and 
as much as one twenty-fifth to one twentieth of a line in diam- 
eter, while others are very minute and short. The sides of these 
tubes are marked with a great number of short parallel bars, 
_ placed in rows one above another, and the length of the bars in 
_ the same vertical row is often seen gradually to diminish, (Fig. 
2,) so that the bars are finally reduced to mere. points. 
‘These bars are so placed as to incline slightly, often almost 
imperceptibly, upwards from left to right in all the ferns I have 
examined. The end of one bar is placed close to the end of one 
in the next row, so that the bars form broken spiral lines around 
the cylinder, and as the membrane of the vessel appears to be 
thinnest between the bars, it follows, that when a force is applied 
to tear this membrane, the laceration takes place ina spiral direc- 
tion, and the vessel when thus torn, appears as in Fig. 4, Plate I. 
Vessels torn and uncoiled in this manner have, I presume, been 
mistaken by Link and others for true spiral vessels. This lace- 
_ ration and uncoiling can be effected with so much ease in ten- 
der shoots of Onoclea sensibilis, Adiantum pedatum, Polypodium 
