On the Floating-Roots of Sesbania aculeata, 
Pers. 
BY 
D. H. SCOTT, M.A., Ph. D., F.L.S., 
Assistant Professor in Botany at the Normal School of Science , and Royal School 
of Mines , 
ASSISTED BY 
HAROLD WAGER. 
With Plate XVII. 
S EVERAL aquatic members of the natural order Legu- 
minosae are remarkable for a peculiar development of 
certain of their tissues, leading to the formation of a floating- 
apparatus, which serves to keep the stem or root, as the case 
may be, at the surface of the water. In the genera Aescky- 
nomene and Herminiera it is the secondary wood of the stem 
which is adapted to this function 1 . In Neptunia oleracea , 
Lour., on the other hand, the floating-tissue owes its origin 
to the cortex of the stem. This case has been fully inves- 
tigated by Rosanoff 2 , who has shown that the floating- 
apparatus is here a form of periderm, though differing in 
almost every respect from ordinary cork. My own obser- 
vations on this plant have fully confirmed those of Rosanoff. 
It will be worth while to give a short account of the phe- 
nomena in Neptunia , , as they present many analogies with the 
case of Sesbania , which forms the special subject of this 
paper. 
1 See De Bary, Comparative Anatomy of the Phanerogams and Ferns, Eng. Ed. 
p. 500. 
2 Ueber den Bau der Schwimmorgane bei Desmanthns natans , Willd., in Bot. 
Zeitung, 1871. I am indebted to Mr J. G. Baker, F.R.S., of Kew, for information 
as to the synonyms of this plant. Desmanthns natans , Willdenow, is the Neptunia 
leracea of Loureiro, and was originally described by Roxburgh as Mimosa natans. 
[Annals of Botany, Vol. I. Nos. Ill and IV. February 1888.] 
