230 



EMBRYOGENESIS IN PLANTS 



(b) not doing so. The terminal cell (i) may divide longitudinally, or (ii) 

 transversely, either (a) not contributing to the suspensor or (b) con- 

 tributing to it. The several possible developments of the basal and 

 terminal cells may be combined in various ways. Now, if we begin with 

 an elongating zygote in which the partition walls are laid down in 

 general conformity with Errera's law of cell division by walls of minimal 



Fig. 54. Capsella bursa-pastoris 

 Later stages in the development of the embryo (after SchafTner). 



area (modified in different species in relation to the gene-determined 

 metabolites present), then the several patterns of development indicated 

 above are what we might expect to find in a survey of a varied and 

 considerable assemblage of species. 



THE SOUEGES SYSTEM OF CLASSIFICATION 



On the basis of extensive investigations of angiosperm embryos, 

 Soueges has outlined a system of classification of embryonic develop- 

 ment based on the mode of segmentation (in particular, see Soueges 

 1937, 1938, 1939, 1949, 1951). In this scheme four emhryonomic types 

 are recognised: (1) fundamental types or archetypes; (2) secondary or 

 derivative types; (3) superposed types; (4) irregular types. The first 

 three are definable by the laws of embryonomy {see below), but the 



