CHAPTER 12 

 EXPERIMENTAL EMBRYOLOGY 



As mentioned in the first chapter, modern embryology seems to 

 comprise three main disciplines. The first, or descriptive embryol- 

 ogy, is a study of the various developmental processes that take 

 place in a plant from the initiation of the sex organs to the matura- 

 tion of the embryo. The second, or phylogenetic embryology, at- 

 tempts to evaluate these data in determining the interrelationships 

 of the different orders and families with a view to improving the 

 existing schemes of classification. The third, or experimental em- 

 bryology, is concerned with an imitation and a modification of the 

 course of nature, with a view to understanding the physics and 

 chemistry of the various processes underlying the development and 

 differentiation of the embryo, so as to bring them under human 

 control to the furthest extent possible. 



In attempting to summarize the present position of the subject 

 of experimental embryology, it seems convenient to discuss it under 

 the following topics: control of fertilization; embryo culture; in- 

 duced parthenogenesis; production of adventive embryos; and in- 

 duced parthenocarpy. 



Control of Fertilization. 1 Ever since the rediscovery of Mendel's 

 laws in 1900, breeders have been increasingly active in crossing 

 different varieties, species, and genera with a view to producing 

 newer and more useful types. However, their attempts are often 

 thwarted by one or more of the following difficulties: (1) disharmony 

 in time of flowering of the two parents ; (2) failure of pollen to germi- 

 nate on the stigma; (3) slow growth of pollen tubes; (4) bursting or 

 dying of pollen tubes in the style ; and (5) inability of the sperms to 

 effect fertilization. 



Of these, the first is largely a physiological problem. A dis- 

 harmony in the time of flowering of the two parents can be partially 

 overcome by altering the environmental conditions, chiefly tempera - 



1 For further information on some aspects of this problem, see Blakeslee (1945) 

 and Maheshwari (1950). 



375 



