. Botany for agricultural students . Botany. 220 GROWTH OF STEMS Indirectly light is very essential for growth because of its im- portance in the manufacture of plant foods. But directly light has little effect, unless it is intense, and then it checks growth. That most plants grow faster at night than in day time is well known; and, although much of the increase in the rate of growth at night is due to the greater humidity of the air, some is due to the absence of the inhibitive effect that the sun's rays have on. Fig. 200. — Pines growing in the open where their trunks are short and much bra
. Botany for agricultural students . Botany. 220 GROWTH OF STEMS Indirectly light is very essential for growth because of its im- portance in the manufacture of plant foods. But directly light has little effect, unless it is intense, and then it checks growth. That most plants grow faster at night than in day time is well known; and, although much of the increase in the rate of growth at night is due to the greater humidity of the air, some is due to the absence of the inhibitive effect that the sun's rays have on. Fig. 200. — Pines growing in the open where their trunks are short and much branched. From Bulletin 24, North Carohna Geological and Economic Survey. growth. In Bacteria, where the protoplasm is not protected by pigments, the sun's rays so inhibit growth that they have an im- portant germicidal effect. On the other hand, if plants do not have sufficient light, they are affected in various ways. For example, when plants are grown in the dark, as the Potatoes in Figure 198 illustrate, the stems are excessively elongated, the leaves are abnormal, and the plant lacks chlorophyll, on which account the plant is said to be etio- lated. Even plants grown in the shade, having the light only par- tially cut off, are usually taller and more slender than plants. 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 Martin, John N. (John Nathan), b. 1875. New York : John Wiley & Sons, Inc.
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