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 POLYEMBRYONY AMONG ABIETINEAE 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 261 



John T. Buchholz 

 (WITH FIFTEEN FIGURES) 



Polyembryony among conifers is of two kinds : cleavage poly- 

 embryony, in which a single fertilized egg gives rise to many 

 embryos; and the simple polyembryony, which is due to plurality 

 of archegonia. This latter form is encountered wherever there are 

 several eggs that may be fertilized, and therefore is found among 

 all gymnosperms. The fact that polyembryony was found in both 

 the pines and the cycads, and was due to plurality of "corpuscula" 

 or "areolae" (archegonia) in both instances, was one of the argu- 

 ments presented by Brown (i, 2) as early as 1826 as showing a 

 fundamental relationship between these two groups. 



A form like Pinus, which has cleavage polyembryony, usually 

 has several eggs fertilized also, and therefore combines both forms 

 of polyembryony. Since each zygote in Pinus usually gives rise 

 to a system of 8 embryos, there may be as many embryos as 8 times 

 the number of fertilized eggs. If all 6 of the archegonia of some 

 species were fertilized, 48 embryos might be produced, but ^is the 

 maximum number of embryo systems that have actually been found, 

 and even then many of the embryos disappear very early, some of 

 the rosette embryos being aborted without division of the embryo 

 initial cell. 



In discussing polyembryony, it is necessary to consider briefly 

 the pine proembryo stages, shown in the accompanying figures. 

 The writer's interpretation of the facts brought out by various 

 investigators, together with his own studies, would describe the 

 initial steps in the development of the pine embryo as follows. 



The zygote begins development with free nuclear divisions 

 ^.(figs. 1-3). When 4 free nuclei have been formed they descend to 

 ^ifthe bottom of the egg, and there undergo another free nuclear divi- 

 sion, after which the primarv embrvo initial group of cells (p) is 



T^4 153] [Botanical Gazette, vol. 69 



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