ASCIDIA. 



313 



an expanded and excavated structure, when the stem 

 or some portion of it is 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 Nelum- 

 bimn, there is but little difference. 



In cabbages and lettuces there not unfrequently 

 occurs a production of leaf-hke 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 httle 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. 



Fia. 167. Lettuce leaf, bearing on the back a stalked cup, arising 

 from the dilatation of the stalk (?). 



