. Principles of modern biology. Biology. very few species, at least among poikilo- thermic organisms, that have extended their range of habitat widely enough to include all kinds (tropical, temperate, and frigid) of climatic conditions. Lastly, some organisms display a capacity to become dormant during periods of very low or high temperature, and frequently the dormant protoplasm is especially adapted for enduring adverse conditions. This is espe- cially true of seeds, spores, and cysts, which sometimes remain alive after they have been exposed to subfreezing or near-boiling tem- peratures. Us
. Principles of modern biology. Biology. very few species, at least among poikilo- thermic organisms, that have extended their range of habitat widely enough to include all kinds (tropical, temperate, and frigid) of climatic conditions. Lastly, some organisms display a capacity to become dormant during periods of very low or high temperature, and frequently the dormant protoplasm is especially adapted for enduring adverse conditions. This is espe- cially true of seeds, spores, and cysts, which sometimes remain alive after they have been exposed to subfreezing or near-boiling tem- peratures. Usually such a great temperature resistance indicates that the protoplasm has undergone reorganization. The cells elimi- nate part of their normal water content, and in a partially dehydrated condition the pro- teins are less susceptible to denaturation by low and high extremes of temperature. Light. Almost all the radiant energy re- ceived by the earth comes from the sun, and if the sun grew dim, all parts of the world would become too cold for the survival of any living thing. Light striking the earth is transformed mainly into heat, and this main- tains the environmental temperature. But a small fraction of sunlight provides energy for the growth of green plants. And since organic compounds synthesized by plants are essen- tial for the sustenance of virtually all other organisms, the importance of light in the general economy of life cannot be overem- phasized. A competition for light among green plants is a primary factor in their struggle for ex- istence. Treelike species survive by over- shadowing their smaller competitors, al- though sometimes a smaller species, by dint of numbers, will pre-empt a certain region, making it difficult for the seedlings of a larger species to gain a foothold. Small annual plants may also succeed in growing on the floor of very dense deciduous forests, but such plants tend to sprout very early in the springtime and to produce their seeds befor
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Keywords: ., bookcentury1900, bookcollectionbiodiversity, booksubjectbiology
