294 
N. Bancroft. 
IV. The Probable Manner of Evolution of the Monocoty¬ 
ledons from a Dicotyledonous Stock. 
If it is agreed that Monocotyledons have evolved from a 
dicotyledonous ancestry, a further problem presents itself, concern¬ 
ing the manner of their evolution from the parent stock, and the 
cause of their breaking away from it. Here again, considerable 
difference of opinion is encountered, and in this case, the differences 
appear to be increasing rather than decreasing. 
The main issue depends upon the solution of the problem with 
regard to the derivation of the condition of monocotyly from the 
condition of dicotyly. 
As Lotsy (42, p. 624) points out, there are various means by 
which this may have been accomplished, and these may be grouped 
under the headings of Syncotyly and Heterocotyly. It is proposed 
to treat these two processes separately giving as far as possible their 
probable causes. 
1. Syncotyly. Syncotyly—or the fusion of the two cotyle¬ 
dons to form one member—has its chief exponent in Miss Sargant 
(57-62), whose anatomical investigations have convinced her that 
the vascular symmetry of monocotyledonous seedlings may be 
directly or indirectly referred to the same type as that of 
dicotyledonous seedlings in which fusion of the cotyledons has 
plainly taken place. Before proceeding to a special consideration 
of syncotyly, it may be well, perhaps, briefly to summarise Miss 
Sargant’s conception of the Primitive Angiosperm from which she 
derives Monocotyledons. This author accepts Arber and Parkin’s 
idea of the evolution of the Angiosperms (2 and 3), and derives both 
Monocotyledons and Dicotyledons from a race of primitive Angio¬ 
sperms which she would place below the Ranalean plexus in Arber 
and Parkin’s table (see 2, p. 77). Primitive Angiosperms possessed 
characteristics common to both the modern sub-groups: namely, 
secondary growth by means of a cambium ; flowers of Ranalean 
type, Arber and Parkin’s idea of the evolution of the angiospermous 
flower being accepted (2, figs 1, 2 and 4); closed carpels ; endosperm; 
two cotyledons ; and seedlings with tetrach vascular symmetry. 1 
Primitive Angiosperm having two cotyledons, it is necessary to find 
a means of determining how the descendants along one line might 
come to possess only one. It is almost impossible to determine 
this from a study of the development of the young embryo within 
1 For views on the primitiveness (or otherwise) of tetrarchy see Tansley 
and Thomas (72), Thomas (73), Compton (10), Hill and de Fraine (34); see 
also Tausley’s criticism of Miss Sargaut’s theory (71). 
