78 



/'/ t.YT BIOLOGY 



from leaves. As a rule leaves can be distinguished by 

 the following tests: (i) Leaves are temporary structures t 

 sooner or later falling. (2) Usually buds arc borne in their 

 axils. (3 ) Leaves are usually borne at joints or 

 nodes. (4) They arise on wood of the current 

 j'car's growth. (5) They have a more or less 

 definite arrangement. When leaves fall, the twig 

 that bore them remains; when leaflets fall, the 

 main petiole or stalk that bore them also falls. 



Shapes. — Leaves and leaflets are infinitely 

 variable in shape. Names have been given to 

 some of the more definite or regular shapes. 

 These names are a part of the language of bot- 

 any. The names represent ideal or ~. ^_ 

 typical shapes; there are no two \ -.\'(, 



leaves alike and very ' •' cZ^st, 



few that perfectly con- 

 form to the definitions. 

 The shapes are likened 

 to those of familiar ob- 

 jects or of geometrical 

 figures. Some of the 

 commoner shapes are as 

 follows (name original 

 examples in each class): 

 Linear, several times longer than broad, with the sides 



\ nearly or quite parallel. Spruces and most grasses 

 are examples (Fig. 102). In linear leaves, the main 

 veins are usually parallel to the midrib. 

 Oblong, twice or thrice as long as broad, with the sides 



% parallel for most of their length. Fig. 103 shows the 

 short-oblong leaves of the box, a plant that is used 

 for permanent edgings in gardens. 



\y/ 



Fig. 102. — 

 Linear- 

 acuminate 

 Leaf of 

 Grass. 



Fig. 103. — Short-oblong 

 Leaves of Box. 



