Chapter XII 



EMBRYOGENESIS IN GYMNOSPERMS: 

 CONIFERALES AND 'GNETALES' 



CONIFERALES 



THIS very considerable assemblage of gymnosperms is believed to have 

 sprung from a Palaeozoic coniferous ancestry, the latter possibly 

 originating from some proto-pteridophyte stock. The order Coniferales 

 has'been variously classified, the principal families, according to several 

 authors, being set out in the accompanying Table. 



Families in the Order Coniferales 



Florin (1951) considers that, on the basis of the female reproductive 

 organs, all the recent genera usually included among the conifers 

 should be referred to two quite distinct subdivisions — the true Coniferae 

 and the Taxinae. 



In the present survey the writer has followed the arrangement of 

 Buchholz (1946) and Johansen (1950). Technical methods for the 

 examination of embryos have been given by Buchholz (1938). 



Certain features are of very general occurrence in the embryogeny 

 of conifers, in particular, the extensive development of the suspensor 

 and polyembryony. Accordingly, some of the main embryonic develop- 

 ments will first be considered, and this will be followed by a general 

 survey which will aim less at completeness than at a samphng of features 

 of special interest. 



The morphology of the ovule in the Coniferales, with its integument, 

 nucellus, prothallus and archegonia is in agreement with the general 



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