of Sesbania aculeata , Pers. 309 
this stage the appearance presented is that of a young peri- 
derm during the development of the lenticels. In the regions 
where the production of floating-tissue is beginning, the phel- 
logen is more active than elsewhere, producing more numerous 
tangential rows of cells towards the exterior. These cells 
next become rounded, while intercellular spaces appear be- 
tween them. The cells then rapidly elongate, the epidermis 
and the two or three outermost layers of the primary cortex 
are forced outwards, and soon become broken through. The 
cells of the floating-tissue now successively assume their 
mature form, growing greatly in length and often branching. 
Only the ends of the cells and their branches remain in con- 
tact. All these changes, which, as we have seen, were at first 
limited to certain portions of the circumference of the stem, 
ultimately extend all round it ; but in the later stages of growth 
the irregular furrowed surface of the floating-tissue still bears 
witness to its originally unequal development. Eventually, 
towards the end of the period of vegetation, the floating-tissue 
becomes detached, and the remaining denser part of the peri- 
derm acquires suberised walls. Thus a normal cork, of no 
great thickness, ultimately clothes the surface of those inter- 
nodes which were before enveloped in the floating-tissue. 
Those parts of the stem from which this tissue is absent pro- 
duce from the first an ordinary corky periderm. 
The above description is chiefly founded on my own obser- 
vations, which agree closely with those of Rosanofif. The 
conclusions which follow from the facts stated are, that the 
floating-tissue is here morphologically equivalent to the peri- 
derm of other Leguminosae, but that it differs from normal 
periderm in four respects : — (1) The cells do not lose their 
living contents ; (2) their walls do not become suberised ; (3) 
they have large intercellular spaces between them ; and (4) 
it is in these spaces, and not in the cells themselves, that the 
air is contained. 
As already pointed out, the resemblance of the floating- 
tissue, in its earlier stages, to the complementary tissue of a 
lenticel, is very striking. Possibly this may be more than 
