34 



BOTANY 



PART I 



the coniiiion leaf-stalk or on the midrib, then termed the spindle or uhachis, a 

 leaf is spoken of as compound (Fig. 37 iih) ; in all other cases it is said to be simplk. 

 The single, separate divisions of a compound leaf are called leaflets. These 

 leaflets, in turn, may be entire, or may be divided and undergo the same segmenta- 

 tion as single leaves. In this way doubly and triply compound leaves may be 

 formed. Simply and doubly pinnate leaves in which the leaflets are attached to 

 the two sides of the rhachis are of common occurrence. The leaflets are either 

 sessile or stalked ; and sometimes also, as in Rohinia and Mimosa, their stalks 



articulate with the spindle by means of 

 swollen pul villi. The term fed ate is 

 aiijjlied to leaves in which the segments 

 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 



Fio. 35. — Part of stem and leaf of a grass. 

 h, Haulm ; r, leaf-.shcath ; k, .swelling 

 of the leaf-slieath above the node ; s, 

 partof leaf-lilaile ; /, ligule. (Nat. size.) 



Pio. 36.— Bird Cherry (Prunus Avium). Bud- 

 scales (1-3) and the transitio!i forms (4-0) to 

 the foliage leaf (7) ; sp, leaf-blade ; s, leaf-stalk ; 

 nh, stipules. (Reduced slightly.) 



peculiarities in their shape and segmentation, are of use in the detcriiiination of 

 ])lants. 



A system of strands known as the VEINS or NERVES traverses the 

 flat leaf-l>ladc. They project moi'e or less from the surface, esj)ec]'ally 

 on the loAver side where they often form definite ri))s. 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 developed 

 main nerves are present. Lateral nerves spring fi'om the one or more 

 main nerves. 



According to their venation or nekvatuee leaves are described as I'AIIallel 



