VIII 



THE DEVELOPMENT OF SEXUALITY IN PLANTS 



Preview. The beginnings of sex in the algae • Oedogonium • A repre- 

 sentative fungus • Alternation of generations in the plant kingdom • Sug- 

 gested readings. 



PREVIEW 



The one unescapable fact that stands out in the observation of 

 plants and animals in the world about us is the remarkable variety 

 among living things. They range from tiny forms too small to be seen 

 with the unaided eye to huge organisms such as elephants or trees. 



The biologist is not satisfied with random looking. He looks for 

 certain things, tries to interpret what he sees, but as Thoreau once 

 said, "We must look a long time before we can see." One of the 

 striking facts already noted in the Roll Call of forms of life is that 

 both plants and animals may be placed in groups having similar 

 characters, and that these groups arrange themselves in a series of 

 gradually increasing intricacy of structure, which goes hand in hand 

 with an ever increasing complexity in functions. Simple plants or 

 animals do things simply. Almost any part of the one-celled Ameba 

 can do any part of the work of the cell although lacking organs found 

 in higher forms. More refined ways of doing things, and a more' 

 efficient division of work, come with increasing complexity of organic 

 structure. The true investigator is ever alert to find forms that 

 illustrate this increasing division of labor, and is always asking why 

 and how such things come about. Biologists have picked out certain 

 representative forms that clearly suggest certain facts and principles 

 that are worth knowing. It is possible, for example, through the 

 study of some simple forms of organisms, such as the Thallophytes, 

 to discover the beginnings of sexuality in plants. 



The Thallophytes include most of the simplest plants and are 

 divided into two great groups, algae and fungi, the latter containing 

 no chlorophyll. Wliile there are six classes of algae, four, namely, 

 the blue-green, the green, the brown, and the red, are classified 

 largely on color. All of the four groups are essentially water- 

 loving plants, showing in many ways that they are simple and 

 rather primitive organisms. In size they range from tiny uni- 



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