Definition - What does Vein mean?
The leaf vein is the mineral and nutrient delivery system present in leaves. These veins carry the nutrients and minerals absorbed by the roots and transfer glucose that the leaves synthesize to other parts of the plant. Since the vein is important in photosynthesis, it enables the improved growth and crop yield of the vines.
WineFrog explains Vein
Grapevines are relatively easy to grow. They can grow in unfavorable climates and poor soil. They don’t need a lot of water or fertilizers, all of which is possible because grape leaves have netted veins. The netted leaf veins allow nutrients and minerals present in minimal quantities to be effectively distributed throughout the whole plant.
The veins are thin and spread throughout the leaves. Along with absorbing sunlight and stimulating vine growth the leaf veins have another added advantage. The veins also stimulate growth of the leaves, which provide a protective cover around the grapes. As a result, the leaf veins contribute towards improving the quality of the grapes in winemaking.