THE LEAF 157 



175. Veins as water carriers. — Examine a leaf from a 

 stem that has stood in red ink for an hour or two. Do you 

 see evidence that it has absorbed any of the liquid? Cut 

 across the blade and examine with a lens. What course has 

 the absorbed liquid followed? What use does this indicate 

 for the veins, besides the one already noted? Observe the 

 point of insertion on the stem, and examine the scar with a 

 lens : do you see any evidence of a connection between the 

 leaf veins and the fibro vascular bundles of the stem? (Ill, 

 125, 126. Notice where and how the veins end. Are they 

 of the same size all the way, or do they grow smaller toward 

 the tip? Are they separate and distinct, or are they con- 

 nected throughout their ramifications, like the veins and 

 arteries of the human body ? How do you know ? Do you 

 see any of the coloring fluid in the small reticulations be- 

 tween the veins? How did it get there? 



176. The nature and office of veins. — We learn from 173 

 and 175 that the veining serves two important purposes in the 

 economy of the leaf : first, as a skeleton or framework, to sup- 

 port the expanded blade ; and second, as a system of water 

 pipes, for conveying the sap out of which its food is manu- 

 factured. In other words the veins are a continuation of the 

 fibrovascular bundles into the leaves, by means of which the 

 latter are put in communication with the body of the plant. 



177. The relation between veining and lobing. — Com- 

 pare the outline of a leaf of maple or ivy with one of oak or 

 chrysanthemum. Do you perceive any correspondence be- 

 tween the manner of lobing or indentation of their margins, 

 and the direction of the veins? (Figs. 210, 211.) To what 

 class would you refer each one ? 



The lobes themselves may be variously cut, as in the 

 fennel and rose geranium, thus giving rise to twice-cleft, 

 thrice-cleft (Fig. 212), four-cleft, or even still more in- 

 tricately divided blades. 



178. Compound leaves. — Compare with the specimens 

 just examined a leaf of horse-chestnut, clover, or Virginia 



