. Elementary principles of agriculture; a text book for the common schools. three plant materials thatcontain the same elements combined differently. 4. By whatmeans does the plant manufacture complex compounds out ofsimple compounds? 5. Name the elements essential for plantgrowth. 6. Name the most common non-essential elements inplants. 7. What are the proportions of the elements in plants? CHAPTER VIHOW THE PLANT INCREASES ITS SUBSTANCE 46. The Work of Leaves. The leaves are the foodfactory of the plant. Perhaps you have never thoughtto ask why most leaves are flat. You will find a sugges-ti
. Elementary principles of agriculture; a text book for the common schools. three plant materials thatcontain the same elements combined differently. 4. By whatmeans does the plant manufacture complex compounds out ofsimple compounds? 5. Name the elements essential for plantgrowth. 6. Name the most common non-essential elements inplants. 7. What are the proportions of the elements in plants? CHAPTER VIHOW THE PLANT INCREASES ITS SUBSTANCE 46. The Work of Leaves. The leaves are the foodfactory of the plant. Perhaps you have never thoughtto ask why most leaves are flat. You will find a sugges-tion of the answer if you note that their flat facesare usually turned toward the source of the strong-est light. Look at a tree, to note the position of theleaves, as seen from a distance and from among thebranches. This position is an advantage to the leaf incarrying on its work, because it secures the greatestamount of energy from the sunlight for the food-makingprocess. 47. Structure of Leaves. A thin section of a leaf,when examined under a powerful microscope, is seen. Fig. 20. Cross-section of a leaf through a vein, or fibro-vascular , upper surface; us, under surface; o, layer of outside cells forming theepidermis; sp. Stoma; g, water duct; wb, phloem; hlz, wood cells of fib-o-vascular bundle. (28) How the Plant Increases Its Substance 29 to be composed of a great number of cells. The surfacelayer forms a skin, or epidermis, which keeps thecells within fromdrying. () The epi-dermis is intwo layers. Theouter, or cutinlayer, is only a thinmembrane which, whiletransparent, to allow thelight to reach the innertissues of the leaf, isimpervious to second layer is a tier of cellswhich support the cutin layer. Thisepidermis is very efficient in keepinthe water in the leaf. Onside of the leaf, and on bothof some leaves, there are many . -^^^cim^^m^small openings,to let the car-bon dioxid en- ^. „, „ x,. , . ^ , . , Fig. 21. Howtheyoungplant gets its fo
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