Chapter XIII 



EMBRYOGENESIS IN FLOWERING PLANTS: 

 GENERAL SECTION 



INTRODUCTION 



EMBRYOGENESIS in flowering plants has long been a subject of special 

 interest to botanists. Historical accounts are available in the 

 writings of Sachs (1890), Soueges (1934), Johansen (1950), and Mahesh- 

 wari (1950), In the present book, considerations of space make it 

 essential that some selection be made from the vast amount of infor- 

 mation now available. The method adopted here has been to consider 

 the embryonic development of flowering plants in its more general 

 aspects as a first stage, then to sample different orders, families and 

 genera of particular taxonomic or other interest. Embryos showing 

 special features, anomalous and aberrant developments, etc., are then 

 considered. Developments which illustrate the effect of genetical 

 change, or the impact of factors which can be specified, are also 

 examined, together with relevant experimental data. Finally, the data 

 are considered in their causal and phylogenetic aspects. The writer's 

 task has been eased by the comprehensive surveys of angiosperm 

 embryology by Schnarf (1929) and Soueges (1934-1951) and by the 

 recent publication of Maheshwari's An Introduction to the Embryology 

 of Angiosperms (1950), and Johansen's Plant Embryology (1950). 

 Maheshwari's book, written in the tradition of Coulter and Chamber- 

 lain's Morphology of Angiosperms (1903), gives an account of the 

 morphology, histology and cytology of the antecedent events as well 

 as of the embryogeny proper. Readers are accordingly referred to this 

 work for an account of the development of the microsporangium and 

 megasporangium, the male and female gametophytes, fertilisation and 

 endosperm formation. Johansen's book is strictly confined to the 

 details and analysis of the embryonic development and is important in 

 that it affords a comprehensive survey of the embryology in all groups 

 of seed plants. 



THE ENVIRONMENT OF THE EMBRYO 



The environment of the embryo is the embryo sac, the surrounding 

 cell layer, and the tissues of the nucellus and integuments. The ovule 

 may be variously orientated with respect to its stalk, while the embryo 

 sac may be ellipsoidal or elongated, or bent round in various degrees. 



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