. Adventures with animals and plants. Biology. PROBLEM Theories about the Origin of Kinds of Living Things 561 loss of water. Mistletoe has a rootlike structure that grows through the bark of trees enabling it to get water and minerals. The grape and many other vines (Figure 280, page 302) have ten- drils which hold the stems upright. Some plants, such as most lichens (Figure 326, page 375) remain alive even though they may become so dry they can be crushed to a powder. These adaptations can be reasonably explained by assuming that they are the result of mutations which made the mu- tants
. Adventures with animals and plants. Biology. PROBLEM Theories about the Origin of Kinds of Living Things 561 loss of water. Mistletoe has a rootlike structure that grows through the bark of trees enabling it to get water and minerals. The grape and many other vines (Figure 280, page 302) have ten- drils which hold the stems upright. Some plants, such as most lichens (Figure 326, page 375) remain alive even though they may become so dry they can be crushed to a powder. These adaptations can be reasonably explained by assuming that they are the result of mutations which made the mu- tants especially well fitted to get along in their environment. Evolution and how it might occur. The theory of evolution is a complex idea. It states that all living things are related to one another because they all came from the same common ancestors far back in geologic time. It states that new species arose from preceding species of plants and animals that were simpler, that this has been happening since plants and animals first existed on this earth, and that it is still going on. This state- ment of the theory of organic evolution is commonly accepted by biologists. But all biologists do not agree on a theory that can explain hoiv this hap- pened. Most biologists today accept De Vries's theory or modifications of it. This is really Darwin's theory with the idea of mutations and chromosomal changes substituted for the general idea of variations. If you use the five steps of Darwin's theory of natural selec- tion, substituting mutations (germinal changes) for the step "variation," you will have a clear statement of De Vries's theory of the origin of species by mu- tation. Fig. 512 TJ}is insect is called the walking stick. Why? Can you see how its structure helps it to hide fro7n its enemies? (schneider and Schwartz) which is one form of protective adapta- tion. Figures 511 and 512 illustrate striking examples of protective resem- blance in insects. Figure 510 is an ex-
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Keywords: ., bookcentury1900, bookpublisherbostondcheath, booksubjectbiology
