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518 BOTANICAL GAZETTE [JUNE 
growing points or primordia, and that this is followed by a zonal 
development resulting in a cotyledonary ring or sheath of varying 
length. If both growing points continue to develop equally, the 
dicotyledonous condition is reached. If one of the growing points 
ceases to develop, the growth of the whole cotyledonary zone is 
associated with that of the other growing point, and the monocoty- 
ledonous condition is reached. In other words, monocotyledony 
is not the result of the fusion of two cotyledons, or of the suppres- 
sion of one; but it is simply the continuation of one growing 
point on the cotyledonary ring, rather than a division of the growth 
between two growing points. In the same way polycotyledony is 
the appearance and continued development of more than two 
growing points on the cotyledonary ring. In fact, in Cyrtanthus 
four growing points appear at first, which under certain conditions 
might result in four cotyledons. The whole situation has its 
parallel in sympetalous corollas, in which there is zonal develop- 
ment associated with three, four, or five separate growing points, 
which, continuing development, are recognized as petals. 
It follows that cotyledons are always lateral structures arising 
from a peripheral cotyledonary zone at the top of a more or less 
-massive proembryo. This reduces cotyledony in general to a 
common basis in origin, the number of cotyledons being a secondary 
feature. The constancy in the number of cotyledons in a great 
group is no more to be wondered at than a similar constancy in the 
number of petals developed by the petaliferous zone. 
The organization of the stem tip in the seedling is worthy of 
consideration. In the mature seedlings of Agapanthus there is no 
appearance of a stem tip; all of the meristematic tissue at the tip 
of the proembryo is involved in the peripheral cotyledonary 
apparatus and the centrally placed leaves. The stem can be re- 
garded as existing only hypothetically in the siphonostelic cotyle- 
donary plate. Later in the history of the seedling the central 
region of the embryo beneath the leaves elongates and the stem 
structure begins to appear. If the early leaves of a plant are very 
small, an organized stem tip appears earlier in the history of the 
embryo, but it is doubtful whether in Monocotyledons any stem 
structure appears until late in the history of the seedling. In fact, 
