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THE POPULAR SCIENCE MONTHLY. 



stances, but one or two examples will suffice. Perhaps the most 

 familiar vegetable product is starch, certainly interesting since it 

 enters so largely into the daily food of the world. Let us make a 

 thin section of a common potato and examine it for a moment (Fig. 7). 

 See what a multitude of tiny spheres and ellipsoids crowd the cells ! 

 If we apply to our section iodine, we introduce the test of color. 

 The little solids take on a bright-blue tint, and so prove themselves 



Fig. 7. Potato-Cells, containing Stakch-Gkains. 



starch. Now we can see why the potato forms so nutritious an article 

 of diet. During fall and winter starch-grains, such as we have just 

 seen, fill the cells of apple-twigs and of branches of various kinds, and 

 form the basis for that lavish expenditure of plant-force by which our 

 orchards and woods are made glorious in the sudden inflorescence of 

 spring. 



If we make a section of the petiole of a begonia-leaf, we may find 

 cell-contents as remarkable as beautiful. Here are plainly crystals 

 with their symmetrical, angular outline. Some of the mineral sub- 

 stances brought through the plant by currents ascending from the roots 

 have found room in the cells of the leaf-stalk to shoot the rays of 

 minute crystals, and here the crystals lie, sometimes a dozen jewels in 

 a single setting (Fig. 8). 



But the interest attaching to plant-cells does not culminate in chlo- 

 rophyl, nor yet in starch-grains and crystals. The chlorophyl, as we 

 have seen, owes its allegiance to the light, the starch to the chlorophyl, 

 and the crystals to the water and the soil ; but back of all this, and 

 behind all this, though intimately united with it all, is that which owes 

 its homage to none of these which moves all, controls all, uses all, 

 builds the cell-wall, and inhabits it is, indeed, the active principle by 

 which chlorophyl becomes efficient, by which the inorganic is lifted 



