22 



in which the primary nerves are practically straight; when 

 they are curved, the leaf is merely described as having 5, 

 7, or more, basal nerves. When the secondary nerves are 

 curved each one frequently runs into and joins the next secon- 

 dary above it, the junction taking place near the leaf margin. 

 A continuous strong nerve, composed of the ends of the 

 secondary nerves, is thus formed close to the leaf margin. 

 This is called a marginal, or intramarginal, nerve and may 

 be seen in Ficus bengalensis, or Eugenia Jambolana. Such a 

 nerve prevents the leaf blade from being easily torn. A 

 Banana leaf has no such nerve and is quickly torn into strips 

 by the wind. If this were not so the enormous leaf blade 

 would offer great resistance to the wind and the plant's 

 tissues would be subjected to a dangerous strain. As a rule 

 a midrib divides the leaf blade into two practically equal divi- 

 sions. When these divisions are unequal the leaf is said to 

 be oblique, as is the case in Ficus Cunia. When nerves 

 continually fork and divide into two branches of approxi- 

 mately equal size, the venation is called furcate and is charac- 

 teristic of many Ferns, see Fig. 6, Plate IV. 



Leaf margin. 22. The margin of a leaf is said 



to be entire when it is an even line not indented in any 

 way, serrate when with sharp teeth directed towards the 

 leaf apex, bi-serrate when each main tooth is again serrated, 

 serrulate when serrate with very small teeth, ruminate 

 when serrate with the teeth directed backwards, dentate or 

 toothed when the teeth are triangular and directed out- 

 wards, crenate when with rounded teeth, repand when it is 

 a gently undulating line, sinuate, or undulate, when the 

 undulations are more pronounced. When the margin is 

 fringed with fine and close-set hairs it is ciliate, and when it 

 is cut into a number of long narrow segments it is fimbriate. 

 W'hen the incisions are deeper, but do not extend more 

 than half-way to the midrib in the case of a penninerved 

 leaf, or to the base of the blade in the case of a palminerved 

 leaf, the leaf is said to be lobed or cleft, according as the leaf 

 divisions, or the spaces between them, are broad and rounded 

 or narrow and acute. W T hen the incisions extend still deeper, 

 the leaf is said to be partite, or parted, and when they reach 

 the midrib or base of the blade, thus dividing the leaf into 

 distinct parts, the leaf is said to be divided. In this case the 

 parts so divided off are called segments and they cannot be 

 separated from the midrib or petiole without the lamina being 

 torn. When each of these divisions has a separate insertion 



