6

22 UMBILICNL VESSELS:'Secr. Il T2, 3;

vifible many days before the flower opens, and in confequence before they are impregnated, as obferved by Spallanzani.

2. The egos of birds contain a bag of air at their broad end for the purpofe of oxygenating the blood of the chick. In this one circum-

ets. os of birds, as

ftance the feeds of plants feém to differ from‘the egg

they contain no air-bag, though it is probable they may agree with the fpawn of ffh, which I fuppofe pofñefs no included air. When the fceds fall on the ground in their natural ftate of growth, or are buried an inch or two beneath the foil, which has recently been turned over, and thus contains much air in its interftices, their coats do not continue dry like the fhells of eggs during incubation, but immedi- ately become moift membranes, like the external membrane of the fpawn of fifh immerfed in water, and in confequence can admit the oxygenation of the air through them to an adapted fet of arteries on their internal furface, according to the curious obfervations of Dr, Prieftley on the oxygenation of the blood by the air through the moift membranes of the lungs.;

It fhould be here obferved, that many feeds, before they fall on the moift earth, are included in a bag of air, as thofe of the ftaphylea,

ladder-nut; of the phyfalis alhekengi, winter-cherry; of colutea, bladder-fenna; in the pods of peas and beans; in the cells furround- ing the feeds of apples and pears; and in the receptacle of ketmia, which probably ferves to oxygenate the blood of the infant feed, which in thefe plants may thus be of forwarder growth, before it is fhed upon the foil.

3. There exifts a feries of glands, and their duéts, improperly called umbilical veflels by fome writers, which fupplies the feed with nourifhment from the parent plant, fo long as it adheres to the ova- rium of its mother, as the veflels by which a pea adheres to the pod, in which it is included; in fruits and nuts, where the kernel is covered with a ftone or fhell, a long cord of veflels pafles into the bottom of the ftone or fhell, and rifing to the top bends round the lobes of the ker-

L ne},

n

mm