

166 BOTANICAL GAZETTE [February 



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2 . The cleavages which separate the 8 embryos from each other 

 are the free nuclear divisions of the proembryo. In forms without 

 cleavage poly em bryony (Picea, and as far as we know concerning 

 other forms), cell divisions homologous with those in Pinus occur 

 in the proembryo. 



3 . The embryos of the Abietineae may be arranged in an inter- 

 grading series, with Pinus at one end and Pseudotsuga at the other, 

 on the basis of the occurrence of cleavage polyembryony, rosette 

 embryos, and the apical cell. The rosette embryos and their 

 vestiges, the rosette cells, are gradually eliminated as we pass from 

 Pinus to Pseudotsuga. 



4. Cleavage polyembryony, rosette embryos, and the apical 

 cell mark a primitive type of embryo development. 



5 . The embryo development of this group shows how the apical 

 cell was lost in the evolution of the Abietineae. 





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6. On the basis of embryogeny Pseudotsuga is unique and is 

 entitled to rank as a separate genus. 



This study was begun at the Hull Botanical Laboratories in 

 the summer of 191 7 and is the result of a preliminary study of the 

 embryo material of these conifers. More detailed descriptions 

 of the embryos with illustrations will appear later. The writer 

 takes pleasure in acknowledging his indebtedness to Dr. C. J. 

 Chamberlain for valuable council in getting this investigation 

 under way. 



University of Arkansas 

 Fayetteville, Ark. 



