Observations 07i the Vascular System of Ferns. 115 



with great ease when the plant is youngs but with more difficulty 

 in the adult plant. The uncoiled duct, when examined by a low 

 magnifying power, has all the appearance of a common spiral 

 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 parallel rows of 

 short bars. 



To obtain these ducts separate from each other, so as to allow 

 the state in which they exist in the plants to be seen, I macera- 

 ted in water for several weeks the bundles of vessels from the 

 petioles of young and tender, though large. fronds of Onoclea 

 sensibilis, Osmunda cinnamotnea, &^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 forc- 

 ing them apart with the points of fine needles. The vessels, as 

 prepared in this manner, present the appearance of long cylindri- 

 cal (Fig. 3, 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 shghtly, 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 in a 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 fe?i- 

 rfer shoots of O?zoc/ea sensibilis ^ Adiantum pedatum, Polypodiwn 



