BOTANY 



occurrence. The leaflets are either sessile or stalkeil ; and sometimes also, as in 

 Knit!, tin and Mimosa, their stalks articulate with the spindle by means of swollen 



pulvini. The term I-EDATK is ap- 

 plied to leaves in which the seg- 

 ments are further divided on one 

 side only, and the new segments 

 are similarly divided (Fig. 38 I). 

 Variations in the outline of leaves, 

 whether they are entire, serrate, 

 dentate, crenate, incised, etc., as 

 well as peculiarities in their ,-hapc 

 and segmentation, are of use in the 

 determination of plants. 



A system of strands 

 known as the VEINS or 



Flo. 35. Ranunculus aquatilis. ub, Submerged leavs ; 

 sb. floating leaves ; l>, flower ; /, fruit. (Reduced.) 



NERVES, traverses the flat leaf-blade. They 

 project more or less from the surface, especi- 

 ally on the lower side 'where they often 

 form definite ribs. Frequently the nerve 

 in the median line of the lamina is more 

 strongly developed and is then termed the 

 midrib ; in other cases several equally de- 

 veloped main nerves are present. Lateral 

 nerves spring from the one or more main 

 nerves. 



According to their VENATION or NEUVATUUE 

 leaves are described as PAUAU.KI, VEINED or NETTED 

 VEINED. In parallel venation the veins or nerves 

 run either approximately parallel with each other 

 or in curves, converging at tfie base and apex of the 

 leaf (Fig. 36 s) ; in netted veined leaves (Fig. 190) the veins branch olf from one 

 another, and gradually decrease in size until they form a fine anastomosing 

 network. In leaves with parallel venation the parallel main nerves are usually 



l-'iu. ::i''. -Part of >tem and leaf <if 

 ;i .urass. //, Haulm: r, leaf- 

 sheath ; k, swelling of the Irut- 

 sheath above the node ; s, part 

 of leaf-blade ; /, ligule, (Nat. 

 sixe.) 



