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III 



The Structure and Function of Higher Plants 



Man's primary interest is, understandingly enough, in man. As the world 

 draws closer together, as food problems change from national to 

 international problems, science has turned more and more attention to 

 plant life, for it is upon the carbohydrate and oxygen-producing capacity 

 of the chlorophyll-bearing plant that animal life depends. The layman 

 may well be forgiven his astonishment when he learns that some 80,000 

 botanists are engaged in solving the riddles of the plant world and thus con- 

 tributing, directly or indirectly, to human welfare. The botanist stands 

 not only at the core of the food, clothing and shelter problem but fre- 

 quently is found fighting the front line battles against plant diseases. 



Like animals, plants range from single-celled to many-celled structures. 

 Simplest of the plants are the viruses, bacteria, yeasts, and certain algae. 

 They are called simple because they are single-celled and lack root, stem 

 and leaf. One of the interesting things about the bacteria and the simple 

 algae is that they have been found in the oldest rocks and so are extremely 

 old phylogenetically. The fact that many of these simple forms reproduce 

 by binary fission or splitting means that the present individuals are cyto- 

 plasmic and in some cases nuclear descendants of the first cells to appear 

 on this earth. This might be termed immortality. 



Leaving the single-celled plants, we note more complex arrangements — 

 some are mere aggregations of independent cells stuck together, others 

 show slight differences in form of cells and indicate a type of speciahzation, 

 a division of labor. Many of the fungi and algae are tremendously com- 

 plex, as for example the huge puffball and the giant brown algae, the latter 

 growing in the oceans to a length of several hundred feet, with root-like and 

 leaf-like structures. From the one-celled green alga to the billion-celled 

 redwood tree, towering three hundred feet or more, is quite a contrast. 



Plant physiology is the science which deals with the functions of plants, 

 their growth, metabolism and kindred subjects. These scientists have been 

 studying for years the formation of sugar, of starches, of rubber, of chicle, 

 of oils in plants. Lately this study has taken a very interesting and vital turn. 

 Botanists are now studying the formation of anti-bacteria, anti-spirochaete, 

 and anti-protozoan substances by plants. Some of these important products 

 are already known to you as penicillin, streptomycin, tyrothrycin and 

 gramicidin. Again plants are furnishing man with life-saving substances 



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