EVOLUTIONARY STATUS OF POLYCOTYLEDONY 
109 
stages in the fusion of two cotyledon primordia to form single broad coty- 
ledons, some of which are shown in figures 1,2, and 3. In this species, the 
fusion is not always complete until after the cotyledons have begun to elon- 
gate, thus making its recognition as a process of fusion very certain. 
Since this work on the pine embryo, the writer has been studying the 
embryos of a number of other conifers. Several species among other genera 
were found in which the cotyledons fuse in the primordial stages much as 
they do in Pinus, while still others were studied in which this performance 
has been completely eliminated from their ontogeny. However, no in- 
stances were found in which a small number of cotyledon primordia gave 
rise to a larger number of cotyledons. 
Another good example of cotyledonary fusion may be found in Picea 
mariana. The material used in this study was sent to the Hull Botanical 
Laboratory from northern Wisconsin (Oneida County) about the first of 
August 191 7. Through the kindness of Dr. George D. Fuller, the writer 
secured a number of cones from this collection. The specimen included 
the upper three feet of a black spruce tree unusually well laden with cones. 
Only one collection was available, and when the seeds proved to contain 
embryos in the cotyledon primordia stage, several hundred of them were 
dissected out under a binocular dissecting microscope and preserved in 
formalin-alcohol. 
The drawings were made under the low power of a compound microscope 
with an Abbe camera lucida. Figures 1-3 and figures 24 and 25 are from 
stained permanent preparations; all of the remaining figures were made 
from the unstained embryos. In the figures, the stem tip primordium was 
shaded slightly so that it might be easily distinguished from the primordia 
of the cotyledons. The embryos are turned with their stem tips up because 
they are more easily handled in this position under the binocular dissecting 
microscope, the suspensor furnishing a convenient means of tilting, turning 
them over, and otherwise handling them without injuring their tips. 
From the first, the writer was impressed by the large number of in- 
stances in which the sinus between two adjoining primordia seemed to be 
disappearing, resulting in a single broad cotyledon. By reference to the 
accompanying figures 4, 5, and 6, it will be noted that these primordia 
fuse very early, before there is any well marked elongation of the cotyledons. 
In many cases this fusion was so striking that it could easily be noticed, 
but in others it was less marked. To see these primordia distinctly, it was 
nearly always necessary to study the contour of the embryos as they were 
held in a slanting position and turned on their long axis with the apex 
pointing awa^^ from the observer. This avoids confusing the stem tip with 
the cotyledons, and makes young and obscure cases appear more distinct. 
The writer realized that some of his readers would be inclined to take 
exception to conclusions based alone on appearances, as shown by the draw- 
ings of these embryos. Figures 4 and 6 might be looked upon as showing 
