Chapter I 



SCOPE AND OUTLOOK 



AN embryo was originally defined as 'the offspring of an animal 

 /\ before its birth (or emergence from the egg),' or, as applied to 

 plants, 'the rudimentary plant contained in the seed' (1728) {Oxford 

 Dictionary). In ferns, however, there is no seed; nor is there a well- 

 defined resting stage, marking the completion of the embryogeny, such 

 as we find in a dicotyledon. On the contrary, the fern embryo grows 

 and develops without interruption until it emerges from the gameto- 

 phyte tissue and becomes established as a free-living sporophyte; and 

 similar developments are characteristic of the embryos of other 

 Archegoniatae. Some elasticity in the use of the term is therefore 

 desirable. There are also occasions when it may be useful and desirable 

 to extend the survey of development beyond the strictly embryonic 

 phase. The terms embryo and germ have come to connote the initial 

 developmental phase in all classes of plants and it is with a compre- 

 hensive survey of this kind that this book is concerned. Since germs 

 may develop from spores as well as from fertihsed eggs, the scope and 

 flexibihty of treatment thus afforded will admit of comparisons being 

 made of the early developments of the sporophyte and gametophyte 

 generations of archegoniate plants, and of thallophytes and vascular 

 plants. Such a survey should both broaden and render more critical our 

 knowledge of embryogenesis, i.e. the inception and formation of the 

 embryo or germ. This may perhaps appear an undesirable extension of 

 the conception of embryology but it is justified by the facts and by the 

 interest of the inferences that can be based on them. This survey, then, is 

 concerned with all classes of plants, and not simply with the Embryo- 

 phyta, i.e. organisms with an enclosed or contained embryo (comprising 

 archegoniate and seed plants), as defined by Engler and by Campbell. 

 There are many reasons, both general and particular, why such a 

 survey should be made, especially at the present stage in the develop- 

 ment of botanical science. In any undertaking, it is wise counsel to 

 begin at the beginning; and so it is in the study of plants. There is, of 

 course, no absolute beginning, for life is essentially a continuous 

 process. But, in all classes of plants, there is a recurring sequence of 

 phases. Those phases which have their inception in the germination 

 of a spore, or in the development of a fertilised ovum, constitute new 

 beginnings and afford the botanist opportunities for investigating the 



