from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Botany A pitcher-shaped or bottle-shaped part or organ, such as the hollow tubular leaf of a pitcher plant.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A pitcher-shaped or flask-shaped organ or appendage of a plant.
- n. One of a genus of simple ascidians, which formerly included most of the known species; sometimes used as a name for the Ascidiidae, or for all the Tunicata.
from the GNU version of the Collaborative International Dictionary of English
- n. A pitcher-shaped, or flask-shaped, organ or appendage of a plant, as the leaves of the pitcher plant, or the little bladderlike traps of the bladderwort (Utricularia).
- n. A genus of simple ascidians, which formerly included most of the known species. It is sometimes used as a name for the Ascidioidea, or for all the Tunicata.
from The Century Dictionary and Cyclopedia
- n. [Also less prop. Ascidia.] A genus of tunicates, typical of the principal family of the class Ascidia, some of whose species are known as sea-squirts: synonymous with Phallusia.
- n. [lowercase; pl. ascidia (-ä).] In botany: Any tubular, horn-shaped, or pitcher-like formation, arising usually from the union of the margins of a leaf or other organ, or from the disproportionate growth of some part.
It is not in all cases easy to trace the origin and true nature of the ascidium, as the venation is sometimes obscure.
It appeared from some transitional forms that the adventitious leaflet, just mentioned, was due to the exaggerated development of this gland, but no clue was afforded as to the origin of the ascidium.
The more distant the  lobes, the deeper the ascidium will become.
They are narrower than those of the teasel, but this depends, as we have seen for the "one-leaved" ascidium, on the shape of the original leaf.
Interrupted leaves, with an ascidium on a naked prolongation of the midvein, are by no means limited to the _Croton_ varieties.
This tube must bear at its summit the conical ascidium produced by the two connate limbs.
By this contrivance the double ascidium assumes a terminal position.
 Likewise we must refrain from a consideration of the physiologic qualities of the tendril, and confine our attention to the combination of a limb, a naked midvein and an ascidium.
Though it is of course conceded that the ascidium of _Nepenthes_ has many secondary devices which are lacking in _Croton_, it seems hardly allowable to deny the possibility of an analogous origin for both.
I have alluded to these cases more than once, but on this occasion a closer inspection of the structure of the ascidium is required.