8 Sargant . — Theory of the Origin of Monocotyledons 
Whether the Monocotyledons as we know them now are 
descended from one such race, or have branched off in this 
way at several distinct periods and from different dicotyle- 
donous stocks, must remain an open question for the present. 
OBSERVATIONS ON THE ANATOMY OF 
SEEDLINGS. 
Part I. Monocotyledons. 
A. Liliaceae. 
The species cut and completely examined from this family 
amount to sixty, representing thirty-five genera. Of these, 
forty-five species, representing twenty-six genera, belong to the 
four central tribes : Asphodeleae, Allieae, Scilleae, Tulipeae. 
Three complete series of sections from the transitional 
regions of three seedlings, differing somewhat in age, have 
been examined and kept for reference before the final notes 
on any species were compiled. Where the first seedlings cut 
have shown considerable diversity of structure, more speci- 
mens have been examined : in some cases details of seven, 
eight, or nine seedlings are included in the notes. 
The series of sections have always been followed from the 
cotyledon downwards through the hypocotyl into the primary 
root. This I have found in practice more convenient than 
working upwards from root to stem. But the lignification of 
the traces is usually at its maximum about the middle of the 
transitional region, and in general proceeds upwards and 
downwards from that level. 
Many observers have remarked that the limits of the 
hypocotyl differ according as they are defined by external 
or internal characters. In this paper I am concerned chiefly 
with the internal anatomy of the seedling, and I therefore 
define the upper limit of the hypocotyl by the insertion of 
the plumular traces on those of the cotyledon, and its lower 
limit by the formation of a stele with complete root- 
characters. 
