244 EMBRYOGENESIS IN PLANTS 



monocotyledonous families, the Juncaceae and Liliaceae. In the 

 Asterad type are included embryos from families of Ranales and 

 Magnoliales and from monocotyledonous genera. In the Lamiales, 

 Gramineae and Liliaceae, both Onagrad and Asterad types have been 



reported. 



In his comprehensive survey of angiosperm embryology, Johansen 

 (1950) has attempted to assign each investigated species to its em- 

 bryonomic type, or variation of a type. This, indeed, appears to have 

 been the main object in the angiosperm section of his book. But 

 having done this, there is no general discussion of the data in their 

 phylogenetic application. He notes briefly that the data of special and 

 comparative embryology 'follow phylogenetic lines more or less but 

 there exists a certain degree of overlapping since species in very diverse 

 and totally unrelated taxonomic families may follow the identical 

 embryonomy' (p. 93). It may therefore be inferred that if the data of 

 angiosperm embryology have any value in phylesis, that value is 

 obscure and is unlikely to be revealed by morphological studies alone. 

 When Maheshwari (1950) considers the relation between embryology 

 and taxonomy, the development of the embryo is only one of his 

 twelve embryological criteria of comparison, all the others being 

 concerned with the inception of the male and female gametophytes 

 and the details of fertilisation. These other embryological criteria are 

 those which have proved of value in settling problems of taxonomic 

 relationship, the details of the actual embryonic development having 

 been used to a very limited extent only. 



Soueges has expressed the view that because of the difficulty of 

 ascertaining the relationships of plants on the basis of their adult 

 form and structure, these being greatly affected by extrinsic factors, an 

 attempt should be made to discover what relationships they show 

 during development. As the early segmentations of the embryo are 

 mainly determined by internal factors, it is reasonable to assume that 

 the comparative study of embryos should be of value in taxonomy. 

 In Soueges view, the unit of classification is no longer the morphological 

 species but the embryonomic type. According to this conception, all 

 the species in a truly related group of plants would have embryos which 

 develop according to identical embryonomic laws. These laws should 

 be restricted to the first four cell generations of the embryo. 



EXAMPLE OF A COMPARATIVE EMBRYOLOGICAL INVESTIGATION 



Lebegue (1952), has tried to establish, on a strictly embryological 

 basis, the taxonomic relations between the Rosaceae and Saxifragaceae, 

 and between these two and other families, e.g. Cruciferae and 

 Resedaceae. In other words, he has asked: Do the embryological data 



