THE LEAF. 



169 



No cases are known of forking in fern-leaves 

 resulting in the formation of two distinct leaves. 



Forked leaves occur perhaps most commonly in 

 plants w r ith their leaves arranged in an opposite- 

 decussate manner. Celakovsky describes a most 

 interesting series of cases in the honeysuckle (Lonicera 

 Periclymenum) , in which all stages between a perfect 

 and entire leaf and the formation of two distinct leaves 

 by means of forking occur (fig. 45 a-c). In the 

 Labiatse they are of common occurrence, and have also 



a b c 



Fig. 45. — Lonicera Periclymenum. Three stages in the division of a 

 leaf by terminal forking-. (After Celakovsky.) 



been seen in the teazel (Dipsacus), the Japan allspice 

 (GJiimonanthus fragr a ns), the oak, and Cardamine pra- 

 tensis; also in the pitcher-plant (Nepenthes sp.), in which 

 one leaf bore two pitchers, the forking having thus 

 affected the pitcher and the extension of the midrib 

 bearing it; in another leaf the green blade was also 

 forked for a short distance. Fig. 46 shows an elm- 

 leaf in which the midrib is completely forked into two, 

 the lamina only partially so. 



The same phenomenon occurs in the leaflets of 

 compound leaves in many plants, e. g. in the scarlet 

 runner (Phaseolus multiflorus) . The terminal leaflet had, 

 by forking, added a fourth leaflet to the usual three. 

 The same author who mentions this also figures a leaf 



