AMERICAN 
JOURNAL OF BOTANY 
Vol. VII April, 1920 No. 4 
EMBRYO DEVELOPMENT AND POLYEMBRYONY IN RELA- 
TION TO THE PHYLOGENY OF CONIFERS^ 
John T. Buchholz 
A consideration of embryogeny has played an important part in nearly 
all discussions of phylogeny, but the embryo development of conifers has 
offered so many variations and apparent anomalies that many students of 
Gymnosperms have been in doubt as to whether the embryogeny should 
be considered very seriously in connection with a study of the morphology 
of this group. So far as I know, the question of polyembryony has not 
generally entered into these comparisons, but has been looked upon as an 
extremely variable feature and one of little morphological importance. 
The present discussion is an attempt to take into account both the embryo 
development and polyembryony in making comparisons between the 
embryogenies of conifers, and aims to point out how these features of embryo 
development may prove to be very valuable criteria in arriving at the true 
phylogeny of the Coniferales. 
Since my new interpretation of the embryogeny of conifers involves an 
accurate knowledge of the condition known as polyembryony, it will be 
necessary to consider briefly the events of proembryonic development that 
lead up to and accompany this condition. We will use Pinus as our first 
illustration, because its better known details of development serve as an 
excellent standard of comparison for the other conifers. I expect to show,_ 
further, that the embryogeny of Pinus occupies a very primitive position 
in relation to all conifers whose embryogeny has thus far been described. 
Pinus 
In the proembryo stage of Pinus it is well known that walls appear 
following the mitosis between the four- and the eight-nucleate stages, but 
it should perhaps be emphasized that after these first walls are formed (fig. 
2), the cells of the lowest tier {p) are the initial cells which give rise to the 
four distinct embryos that completely separate from each other. Another 
free nuclear division occurs in the tier of incompletely walled cells above 
^ Invitation address read before the joint session of Section G, A. A, A. S., the Botanical 
Society of America, and the American Phytopathological Society, in the symposium on the 
"Phylogeny of Seed Plants," at St. Louis, December 30, 1919. 
[The Journal for March (7: 83-124) was issued April 17, 1920.] 
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