LEAVES. 



49 



by a leaflet of the Aspidium (Fig. 40). This variety of venation 

 belongs to the ferns^ and is a distinguishing characteristic of 

 this class of plants. 



Fig. 41. 



Fig. 40. 



Fork-veined leaf. 



Parallel -veined leaves. 



(2.) Parallel-veined leaves are those in which the veins pro- 

 ceed from their origin to their termination without any subdi- 

 vision ; the veins being connected by minute, parallel, straight 

 veinlets, passing perpendicularly from one to the other. The 

 veins of this variety either run from the base of the leaf to the 

 apex, as in Corn, the Lily, Grains, and as seen in Fig. 41, a ; or 

 from the midrib to the margin, as in the Canna and Arum 

 Walteri. &c. (Fig. 41, 6). Of this latter variety there are com- 

 paratively few specimens in temperate climates, but they be- 

 come more abundant as we approach the equatorial regions. 

 Parallel-veined leaves are characteristic of monocotyledons. 



(3.) Reticulated or net-veined leaves are those the veins of 

 which branch and ramify in all directions, forming a complete 

 network. (Fig. 42.) This variety of leaves is characteristic of 

 dicotyledonous plants, and they are the most varied in their 

 forms, and comprise the greater proportion of leaves of tem- 

 perate climates. 



88. There are two varieties of venation in the reticulated 

 leaves, occasioned by the origin of the primary veins. If the 

 veins take their rise along the midrib and proceed to the margin, 

 giving the leaf, in structure, a resemblance to a feather, it is called 

 the Feather-veined. When the veins that originate at the base 



To what class of plants do they belong ? What arc parallel-veined leaves ? 

 Examples? What are reticulated veined leaves ? What class of nlauts do 

 they characterize? — 88. How many varieties in reticulated veined leaves! 

 What are feather-veined leaves ? 



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