parts of which are lost; we can determine how many of 

 the parts fit together, and, by analogy, can tell something 

 of the missing ones. The whole method depends on the 

 admission of genetic relationship, a concept that is built 

 up partly by the study of adult structure, partly by the 

 story of the developmental stages, partly, though in bot- 

 any less than in zoology, by the evidence of paleontology, 

 but more vividly than in any other way by the actual 

 behavior of certain plants in the matter of giving rise to 

 new forms. This last consideration is of such great im- 

 portance that we shall come back to it later. 



One type of morphological investigation has to do with 

 the study of life histories of plants, the whole life story 

 from egg to egg again and here we find the morpholo- 

 gist in close relation with the systematist, for upon the 

 results of such researches must largely depend the under- 

 standing of the relationships of the great groups. The 

 morphologist who devotes his time to the study of life his- 

 tories is engaged in the work of tracing the race history 

 of plants from the comparison of the individual develop- 

 ment of more or less nearly related forms. Thus the 

 homologies which have been traced among the flowering 

 plants and their nearest allies among the ferns and other 

 forms indicate to us the probable race history of these 

 groups. It is true that the beginning of this work dates 

 back some decades, but it is still, to a large extent, an open 

 field, and numerous investigators are actively prosecuting 

 research along these lines. For example, the alternation 

 of a sexual and nonsexual generation of plants which has 

 long been known as characteristic of the life histories of 

 higher forms has recently been established among the 

 lower groups, and thus a much clearer view of the whole 

 series of the plant kingdom is being obtained. 



Somewhat separated, and to a large extent needlessly 

 so, is the work of the plant anatomist and histologist. 



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