72 S organ t — Theory of the Origin of Monocotyledons 
in our own day to separate them from other Monocotyledons 
on embryological grounds (Van Tieghem, 44). 
The structure of some Ranunculaceous seedlings in which 
the cotyledons are partially united has already been described 
at length. The similarity between their vascular symmetry 
and that of a type of seedling primitive among the Liliaceae 
has led me to a conception of the Monocotyledonous embryo 
nearly identical with that of Agardh. This comparison has 
already been emphasized, but it must not be supposed that 
such partial union of the seed-leaves is confined to the Ranun- 
culaceae and their near allies. On the contrary, examples of 
such structure are recorded from many families, some widely 
separated systematically from the Ranunculaceae. 
The seedlings in which partial fusion of two cotyledons 
occurs may be divided into two classes of very unequal size. 
In the first, the cotyledons are united by both the margins 
of their petioles. These form a slender cylinder, which is not 
always hollow throughout its length. There is always a 
conical chamber at the base however, within which the 
plumular bud is developed. 
In the second class, the petioles are united by one margin 
only. The double member thus formed is always lateral 
with respect to the plumular axis. 
The formation of a cotyledonary tube in the first way 
has been recorded in a large number of species, but the 
literature of the subject is scattered. The following list 
makes no pretence to be exhaustive. I have included in it 
only those species of which I have seen figures, or descriptions 
sufficiently full to make the facts certain. The- references are 
to such descriptions : in the choice of authorities I have pre- 
ferred the more recent and more easily accessible, and have 
taken no account of priority in discovery. 
