62 PINNATE WITH PSEUDO- PALMATE BASE [CH. 



to the age of the leaf and the season, they can be grouped 

 according to the characters of what we here term the 

 tertiary veins. The secondary ribs of the pinnate venation 

 run from the midrib nearly parallel to one another towards 

 the margins. These give off the tertiaries, which may be 

 parallel curved or straight or not ; if the former he 

 calls them regular, if the latter he calls them irregular. 



The tertiaries are regular in Salix alba L., S.fragilis 

 L. and S. phylicifolia L. They are irregular in S. pur- 

 purea L., S. Babylonica Tourn. and 8. herbacea L. 



I have however been unable to verify these con- 

 clusions, and doubt whether they can be upheld in the 

 cases cited. 



As with pinnate venation, so with palmate venation, 

 several sub-types are recognisable when we pay attention 

 to details. 



Instructive cases, showing how readily the two types 

 of pinnate and palmate venations merge one into the 

 other, are afforded by the Lime and the Plane. In the 

 former (Fig. 21) we see that while the predominant type 

 is clearly pinnate, there are two or three basal secondaries 

 which arise with the midrib at the base of the leaf and 

 diverge at different angles, throwing out strong outer 

 branches so that the venation of this leaf is almost 

 palmate below. It may be appropriately described as 

 pinnate with the base pseudo-palmate. 



In the Plane, again (Fig. 22), while the venation ap- 

 pears obviously palmate at first sight, the two strong 

 lateral ribs diverge from the midrib some little way above 

 the junction with the petiole, and are, strictly speaking, 

 merely the lower secondaries of a pinnate venation. 

 Further examples of the same kind are to be met with 

 in Populus alba, the Birch and elsewhere, and may be 

 referred to as pseudo-palmate. 



