Botany and Zoology. 281 
off in the morning were found to be closed; when exposed to the sun for 
several hours they opened again, but closed with rapidity when immersed 
s 
¥ 
when the guardian-cells are exposed to the influence of these agents they 
form such combinations as are able to induce a powerful endosmosis, and 
are more or less decomposed when light is withdrawn; for, as is well 
known, the guardian-cells, like the cells of the parenchyma, contain chlo- 
tophyllaceous matter. 
"i Direct comparative measurements show that the projecting part of 
* the guardian-cells, beyond the anterior cavity, contracts but slightly, so 
that the process is effected chiefly by the change in the form of the 
boundaries of the true opening. : 
The guardian cells expand most in a vertical direction, and thus change 
their transverse diameter from a circular to an elliptical form, so as to 
draw in the thinner portion of the lateral surface which lies free in the 
ag of the stomate. This explains why the opening is not closed 
hen these cells are distended by the water which fills them. 
C. F. Sronz. 
| 2+ On a boring Sponge ; by J. Lurwy, (Proc. Acad. Nat. Sci. Philad,, 
Yul, 162.)—Dr, Leidy also directed the attention of the members to sev- 
- 
perforations were due to some other molluscous animal or @ worm ; and 
uently sought for them. The last summer, in dredging, in 
“utrents from the wider tubes. 
SEConp SERIES, VOL. XXIII, NO. 68.—MARCH, 1857. 
‘ 36 
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