114 ZJSSSOJV^S WITS PLANTS 



125. The leaf of the common moonseed is 

 shown in Fig. 111. This shows a different ar- 

 rangement. The petiole is attached just inside the 

 border or edge of the blade. In the common 

 nasturtium (or tropseolum) of the gardens (Fig. 

 112), the petiole is inserted almost centrally. 

 Leaves in which the petiole is inserted inside the 

 edge of the blade are said to be peltate (that is, 

 "shield-like"). This mode of attachment may- 

 occur even in much -divided leaves. The pupil will 

 recall the may -apple or mandrake. Compare the 

 leaves of water-lilies, and of other plants which 

 have floating leaves. If the leaflets of a digi- 

 tately- compound leaf were to grow together, the 

 leaf would be peltate; but the pupil must 

 determine if true digitate leaves are ever pel- 

 tate. 



126. The petiole, then, has no necessary rela- 

 tion with the leaf in size or in method of at- 

 tachment to the blade ; and many leaves are 

 wholly sessile. A consideration of tapering leaves 

 (as the barberry) suggests that the petiole may 

 have arisen originally as a prolongation and modifi- 

 cation of the midrib, or as the result of an elimi- 

 nation of a part of the blade. The pupil may 

 now inquire what purpose, if any, the petiole 

 serves ; and he should be able to suggest an 

 answer to the question. 



