48 Dr. D. P. Gardner on the 
This rock extends throughout the peninsula, as far south at 
least as T'ampa bay ; and both the east and west shores of this 
peninsula are covered with a Pleistocene formation of recent spe- 
cies of shells and remains of mammalia. The elevation of East 
Florida above the sea level isso inconsiderable, that all or nearly 
all of it must have been submerged at the time the Post-pliocene 
species were existing, and therefore its elevation was contempo- 
raneous with that of the Keys, which — its. ee apuiliersy 
and western coasts. — 
‘ 
Arr. VI— The Physical Structure of Plants ; by D. P. Garpyer, 
‘M_D., formerly Professor of Chemistry and Natural Philosophy 
“in Wattipdén Sidney College, Virginia. 
_ 1. Te composition of the earth’s atmosphere is the result of 
great physical laws, which acting in all places produce an uniform- 
ity of structure of the highest interest and importance. What- 
ever cavities or porous systems lie in this medium are subject to 
its laws, and the same forces which produce the diffusion of gas- 
eous volumes into the air, govern their penetration throughout 
membranes. The movement into a cavity, and the escape of 
aériform matter come to an end after a time, and there remains a 
similar atmosphere within, and around the exterior. So true is 
this that whatever gases are confined in porous bodies, pervious 
tissues, or fissured vessels, will sooner or later acquire the com- 
position of the common atmosphere. 
2. Botanists in studying the phenomena of plants, have hitherto 
been too much attracted by those of the highest development, in 
which a complex machinery of spiral vessels, laticiferous ducts, 
and other additional organs exist. The office of these parts will 
undoubtedly be resolved in time, but unless we first comprehend 
the general functions, the uncertainty which now exists in vege 
table physiology will remain undispelled. The green mildew of 
—_ walls, Chlorococcum vulgare, offers us an instance of an 
plant, consisting of a single cell, which is neverthe- 
lend eager: of all the essential qualities of avegetable. With- 
“hmited are stored the forces of growth; the 
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Oe EE ec RO oi, TO, ERT gg 3 1 4 ed 
formed 
~ 
