162 BOTANICAL GAZETTE [February 



! & 



here a very interesting intergrading series, with Pinus at one end 

 and Pseudotsuga at the other. There seem to be but two alterna- 

 tives; either the Picea or Pseudotsuga type of embryo has given 

 rise to the Pinus type with cleavage polyembryony, or the Picea 

 embryo is composite in its origin, being made up of the fused or 

 combined elements that produce the many cleavage embryos in 

 Pinus. 



The writer believes that the pine embryo with its cleavage poly- 

 embryony is the primitive type, and the following are among the 

 reasons for this conclusion. The pine embryo "combines with 

 cleavage polyembryony the apical cell, a primitive character, which 

 clearly recapitulates its semi-pyramidal predecessor at the stem 

 tip of the fern. To assume that cleavage polyembryony is a derived 

 feature would take away all phylogenetic significance from this 



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structure, for the Picea and Pseudotsuga type of embryo have no 

 apical cell. The apical cell could hardly be considered an acci- 

 dental result of the splitting of a Picea-like embryo. This con- 

 ception might be entertained if the terminal cell began to display 

 apical cell characteristics only after separation of the embryos, but 

 a true apical cell has been shown to exist from the embryo initial 

 stage, from the time the first walls appear in the proembryo. 



The apical cell is present in the adult ferns and in the first stages 

 of the pine embryo; it is absent in all adult gymnosperms and like- 

 wise in angiosperms. This structure has been eliminated in passing 

 from the lower to the higher vascular plants, and in Picea , Larix, 

 and Pseudotsuga the apical cell is entirely eliminated from the 

 beginning of the life history. The embryo development in this 

 group shows how the apical cell was lost in the evolution of the 

 Abietineae. 



Another reason why the Pinus embryo must be considered the 

 more primitive type arises from the study of the rosette embryos. 

 In the Picea embryo are found the vestigial rosette cells, which 

 never divide, but are clearly homologous with the rosette embryo 

 initials in the pine. Even in the pine these rosette embryos are 

 vestigial, but since these rudimentary structures are well developed 

 in the latter, one would infer that the Pinus type represents the more 

 primitive condition. 



