. Biology and man. Biology; Human beings. Solidago (goldenrod) Mountain. Atitr Uiuc'iil/er^. Ihv blori/ ol Evolution Aftci Clements INFLUENCE OF ENVIRONMENT UPON PLANTS Effects of excessive sunshine are shown in the first pair of plants. Effects of low tem- perature and excessive loss of water are shown in the second pair. We have come to take chemical influences for granted in all proto- plasmic activities, both as foods and as poisons. We have also come to think of the vitamins and hormones as chemical modifiers of protoplasm. But growth is not the same as development, and the two processes
. Biology and man. Biology; Human beings. Solidago (goldenrod) Mountain. Atitr Uiuc'iil/er^. Ihv blori/ ol Evolution Aftci Clements INFLUENCE OF ENVIRONMENT UPON PLANTS Effects of excessive sunshine are shown in the first pair of plants. Effects of low tem- perature and excessive loss of water are shown in the second pair. We have come to take chemical influences for granted in all proto- plasmic activities, both as foods and as poisons. We have also come to think of the vitamins and hormones as chemical modifiers of protoplasm. But growth is not the same as development, and the two processes are not necessarily influenced in the same way by any particular chemical. Inner Factors Temperature, light, moisture, chemicals, oxygen, and the like influence metabolism in many species. But what is it that brings about differentiation in the first place ? One way of thinking about what happens during the progressive change from a single cell (or a few similar cells) to the many millions of differentiated cells is to follow cell-divisions step by step. When two daughter cells are formed, they are apparently just alike. But if they remain clinging together, each has a surface flattened against the other. These cells are no longer round, the same in all directions. After a second division, the four cells press against one another at different relative parts. After a division takes place in a horizontal plane, the food supply is different for the upper cells from what it is for the lower ones. Each cell comes to be influenced in a different way by pressure, food supply, 358. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gruenberg, Benjamin C. (Benjamin Charles), 1875-1965; Bingham, N. Eldred (Nelson Eldred), 1901-. Boston, New York, [etc. ] Ginn and company
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