. Embryogenesis in plants. Embryology. 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 s
. Embryogenesis in plants. Embryology. 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, 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, 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
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