EMBRYOGENESIS IN GYMNOSPERMS 



197 



Pinaceae has been given by Johansen (1950), following the work of 

 Buchliolz (1918 et seq.). From the causal standpoint the basic questions 

 would appear to include: How do known genetical changes affect (i) 

 the distribution of growth, (ii) cellular differentiation, and (iii) organ 

 formation, in the embryonic development ? 



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M N 



Fig. 43 (contd.) 



ARAUCARIACEAE 



The embryogeny of Araucaria and Agathis is notably different from 

 that of all other Coniferales {see Eames, 1913; Burlingame, 1915; and 

 Johansen, 1950). In Araucaria angustifoUa, the 32-45 free nuclei 

 become uniformly or concentrically distributed through the sub- 

 spherical proembryo. In Agathis the free nuclei number 32-64. With 

 the onset of wall formation in Araucaria, a polar elongation of a 

 curious kind begins : those cells which later will give rise to the embryo 

 proper occupy a central position, with elongated suspensor cells on 

 the micropylar side and a layer of considerably enlarged cap cells on 



