v] 



PINNATE-LOOPED VENATION 



57 



A third form of pinnate venation may be distinguished 

 as follows. The single midrib gives off pinnate second- 



Fig. 17. Leaflet of Walnut, Juglans regia, showing pinnate-looped 

 venation. The secondary ribs b leave the midrib a in pinnate order, 

 but curve forwards (near d and e) and loop with the next in front. In 

 this case the looping is so near the margin that an infra-marginal vein 

 may result, c tertiaries, forming cross-ties and breaking up into the 

 network (Ett). 



