416 PROF. OLIVER ON THE STRUCTURE AND MODE OF DEHISCENCE 
25 inches in length, and about 3} to 3$ inches in breadth about the middle, tapering 
gradually to the base; they are but slightly narrowed towards the apex, which is more 
or less obtuse or rounded. Each valve is about + inch thick in the middle and 3 inch at 
the margin. Plate XXXVII. fig. 3 represents a cross section of a valve, showing the 
thickening towards both sutures. The valves are marked on the outside by numerous 
longitudinal anastomosing ridges, corresponding to the exterior bundles of thick-walled 
prosenchyma. The inner surface is nearly smooth, the direction of the woody tissue which 
covers it being slightly oblique. When the valves are fresh, or after they have been soaked 
in water, they are flat, or nearly so, and, if already separate, they may be applied face to face 
throughout; as they dry their extremities gradually curve outwards, as shown by fig. 1, 
If a small, narrow longitudinal strip be removed from the inner face of the dry, curved 
valve (e. g. the portion marked by the dotted line c d in fig. 2), and soaked for an hour 
or so, it will become flat, without, however, increasing perceptibly in length. There may 
be an increase ; but if there be, it is very slight. If acorresponding strip be removed from 
the outer side of the valve (as enclosed by the dotted line a b, fig. 2), and similarly treated, 
it will be found to increase considerably in length. One of the prosenchymatous bundles 
from the outer layer of a valve, measuring 2 inches in length when dry, soaked in water 
for an hour, gains about ;55ths of an inch. The same strip, allowed to dry gradually by 
exposure in a sitting-room, will nearly lose this increase in twenty-four hours—the rate of 
contraetion depending, of course, upon the dryness of the room. 
I give a few measurements of bundles of this contractile tissue taken from the outer 
portion of a valve. "Phe intervals between the observations were simply those of con- 
venience. From the general character of the observations, it appeared useless to affect 
accuracy by noting temperature, or by expelling the comparatively small amount of 
moisture which must doubtless have been present at the zero from which I reckon, and 
which I took as I found it in specimens which had been kept a few years in a museum- 
cabinet. 
l. À narrow bundle, 2 inches in length when dry, after being soaked in water about 
10 minutes, measured 2:17 inches, 
16 EE] 55 2:25 وو‎ 
52 وو‎ » 201 oos 
: 4$ hours, Á 2399. a 
It did not increase in length after soaking a day or two longer, nor after boiling. 
2. A similar piece, 2 inches in length when dry, in 
5$ minutes measured 2:04 inches, 
42... 5 wane 
41 hours, 35 28 
The same allowed to dry by exposure on a sitting-room table, in 
33 minutes, measured 2:29 inches, 
1 hour 7 HE 
19 hours 5 EM د‎ 
8, One inch long when dry, soaked about 
4j hours, measured 1°17 inch, 
