Factors Influencing the Growth of Plant Embryos 



NANCY KENT ZIEBUR 



THE growth of plant embryos has been the subject of many in- 

 vestigations during the last half century. It is a field of great 

 theoretical interest particularly because of the opportunity that is pro- 

 vided for observing the development of adult structures from the cells 

 that are initially the least differentiated. Two major problems have been 

 considered in this connection. First, how is the embryo fed, which of 

 the surrounding tissues contribute directly to its support, and what is 

 the nature of the food material it receives? Second, to what extent is the 

 pattern of embryonic growth autonomous, what is the role of the other 

 seed parts in the control of embryonic development, and by what 

 mechanisms is this control exerted? Solutions to these problems have 

 been sought through both histological and physiological investigations, 

 and by use of both natural and artificial conditions of growth. 



A histological study by Nutman (8) deals with the evidence for the 

 formation of growth-promoting substances in the developing rye kernel. 

 He observed within the embryo sac and neighboring tissues a series of 

 discontinuous growth phases associated with characteristic degeneration 

 in certaiii parts of the developing fruit. Thus, soon after fertilization 

 the synergids degenerate while simultaneously the antipodals divide; 

 then when the antipodals degenerate, the endosperm nuclei begin to 

 divide near the degenerating tissue, a characteristic nucellar strip under- 

 goes a new development, and the embryo enlarges greatly. As the 

 nucellar strip, in turn, is absorbed, the aleurone layer of the endosperm 

 is formed. Finally, during the same general period a strict time associa- 

 tion may be observed between the appearance of the stem, root, and 



Editor's Note: Paper No. 408 from the Department of Genetics, University of 

 Wisconsin. 



