BULLETIN 



OF THE 



TORRRY BOTANICAL CLUB 



Vol, XVI.] New York, December 10, 1889. [No. 12 



On the Floating-tissue of Nesaea verticiliata (L), H.B.K. 



By Joseph Schrenk. 



Plates XCV-XCVII. 



Nescea verticiliata grows in stout clumps along the swampy 

 borders of our ponds and lakes. In the months of July and 

 August many of the slender, wand-like stems sent up by the 

 root-stock have attained a considerable length (frequently six or 

 eight feet), and begin to bend downward by their weight, until 

 the apex of the stem touches the surface of the water, when it 

 curves upward again (Plate XC V). Very soon we notice a swell- 

 ing around the stem at the region of contact between stem and 

 water, about lo mm. below the apex. The apex continues to 

 grow more or less rapidly, while the swelling below it increases 

 and extends over a distance of from 20 to 40 cm. (Fig. i). 

 oimple roots now make their appearance on the lower side of the 

 internodes lying on the water, which keep growing straight 

 downward, sometim.es to a remarkable length, until, at last, they 



reach the bottom and penetrate into the ground, that portion of 

 the stem over which the swelling has extended remaining 

 floating on the waten 



Meanwhile the epidermis of the stem, at this region, shows 

 longitudinal fissures, and a snowy white, soft, elastic, spongy 

 tissue is seen underneath. At a more advanced stage the roots, 

 having taken a firm hold of the muddy ground, draw the inter- 

 nodes at which the sweUing first appeared down into the water, 

 and the swelling gradually extends over those parts of the stem, 

 both towards the parent rootstock and the apex, which are com- 



