CHAPTER XXXVII 

 HEREDITY IN PLANTS 



Many hereditary resemblances and differences among plants were men- 

 tioned in previous chapters, but the conditions and processes of which 

 they are the results were not analyzed. In the study of plants and ani- 

 mals the terms "heredity," "inheritable," or "heritable" are used to indi- 

 cate that something inherent in the parent is transmitted to its progeny, 

 and influences, or conditions, individual development and behavior of 

 the progeny. The distinctive characters of species, of varieties, and of 

 either general or specific races reappear by development in succeeding 

 generations over long periods of time. The modern species of elms and 

 maples, for instance, still resemble their ancient ancestors that lived dur- 

 ing the Cretaceous period many millions of years ago. The human race 

 as a whole, or anv one of the specific races of man, likewise exemplifies 

 inheritance. 



General Aspects of Heredity 



The term hereditv is quite properly used in several ways : ( 1 ) to refer 

 to the resemblances of plants and animals to their progenitors, or ( 2 ) to 

 designate what is obtained in the fertilized egg from the gametes, or 

 (3) to indicate the whole range of biological processes underlying in- 

 heritance. The sequences of events in heredity that have been discovered 

 and shown by experiment to recur in successive generations are often 

 referred to as the laws of hereditv. Manv of the more fundamental laws 

 of heredity in plants and animals are similar, but the related processes 

 and structures involved in their operation may be quite different. Sev- 

 eral examples of conditions in plants not met with in the study of heredity 

 in animals are: the frequent occurrence of self-fertilization, the preva- 

 lence of vegetative multiplication, the differentiation of reproductive 

 tissue from vegetative (somatic) cells throughout the life of the plant, 

 the two-phase life cvcle, and the development of endosperms in some 

 seeds (Chapters XXXI, XXXIII, and XXXIV). 



Hereditv is not limited to parental resemblances. Among the progen\^ 



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