ASCIDIA. 313 
an expanded and excavated structure, when the stem 
or some portion of it 1s affected. 
The fruit of the rose, the apple, the fig, and many 
others, is now generally admitted to be composed 
externally of the dilated end of the flower-stalk in 
which the true carpels become imbedded. Between 
such cases and that of a peltate leaf with a depressed 
centre, such as often occurs, to some extent, in Nelwm- 
bium, there is but little difference. 
In cabbages and lettuces there not unfrequently 
occurs a production of leaf-lke processes projecting 
from the primary blade at a right angle (see Enation). 
Sometimes these are developed in a tubular form, so 
as to form a series of little horn-like tubes, or shallow 
troughs, as in Aristolochia sipho. At other times the 
nerves or ribs of the leaf project beyond the blade, 
and bear at their extremities structures similar to 
those just described. 

Fic. 167.—Lettuce leaf, bearing on the back a stalked cup, arising 
from the dilatation of the stalk (?). 
