4 EMBRYOGENESIS IN PLANTS 



should sedulously follow the zoologists — indeed, they should be 

 cautious to a fault when applying zoological concepts to botanical 

 phenomena — but it is evident that they can gain inspiration and 

 valuable techniques from them. 



Some early investigators of embryology held the view that ontogeny 

 was a recapitulation of phylogeny. According to the Theory of 

 Recapitulation, the morphological development of the individual 

 affords a record in miniature of the history of the race. This idea has 

 not found much support or favour among botanists and it has been 

 strongly rebutted by some zoologists {see de Beer, 1930, 1950). Indeed, 

 it has been regarded more as an interesting general idea than as a 

 fundamental conception which could be fully accepted. There is, of 

 course, some evidence that seems to support the theory. In the con- 

 temporary view, the many aspects of development are held to be 

 determined and controlled by factors in the genetic constitution, or 

 genotype, of the species. Since the genotype of a contemporary species 

 comprises ingredients of the hereditary constitution of ancestral forms, 

 a study of the ontogeny may reveal the inception and development of 

 both distant ancestral and more recently evolved characters. 



While some major groups of plants afford indisputable evidence 

 of community of origin, there is also abundant evidence of parallel and 

 convergent evolution. The study of the underlying causes of these 

 homologies of organisation may be indicated as one of the most interest- 

 ing and important tasks in biology. The data of embryogenesis may 

 have an important place in the study of this phenomenon. 



The initial embryological studies were essentially morphological in 

 inception and outlook, and indeed this was necessarily so. The aim was 

 to provide a demonstration or record of development from the first 

 division of the zygote up to the point where the embryo could maintain 

 itself as a free-living individual. A great deal of careful and painstaking 

 effort has been necessary to obtain this information; and it may be 

 said, with due emphasis, that these anatomical studies not only show 

 us what the embryos of particular species look like: they constitute 

 the basis on which all further work must rest. Nowadays, however, we 

 recognise that embryology need not, and should not, be pursued only 

 by the methods of the anatomist : we want to know about the factors 

 which determine the observed developments. Many new possibihties 

 are opening up. A new outlook and new investigations have been 

 made possible by recent discoveries in genetics, biochemistry and 

 physiology and by new manipulative techniques, e.g. surgical treat- 

 ments, and the methods of tissue culture. In short, it is the process of 

 embryogenesis, culminating in the organisation of the young plant, 

 that is of paramount interest and importance to the contemporary 



