Evolution of Monocotyledons. 297 
normal fusion of cotyledons by one margin only, and adds that 
fusions are not infrequently found in abnormal specimens of types 
having distinct cotyledons (59, p. 75), such as Ranunculus repens , 
Ranunculus chins and Urtica dioica. These instances suggest that 
the single seed leaf of some other species of pseudomonocotyledonous 
Dicotyledons may have been formed in a similar way (see Sargant, 
59, Table II, p. 76, 77), 1 and, of course, indicate the possibility of a 
similar origin of monocotyly in true Monocotyledons. 
1 Cf. Compton (11, p. 803, footnote 3). 
Miss Sargant next considers the apparently terminal position 
of the single cotyledon in Monocotyledons, maintaining that if it 
“ be derived from the two cotyledons of an ancestor, it cannot really 
be terminal, but must represent the congenital fusion of two lateral 
members” (60, p. 339). In the case of Delphinium nudicaule (60, 
p. 339, figs. 1 and 2), which possesses a cotyledonary tube, the first 
leaf breaks through the tube near its base, and for some time appears 
as though laterally inserted on the cotyledonary axis. But as the 
leafy stem develops, the cotyledons are pushed aside and assume 
their true position as lateral organs. In the case of congenitally 
united cotyledons, a lateral position of the stem-bud is necessary to 
free development. The cotyledons are usually formed some time 
before the growing point of the stem, and naturally, the single 
rudiment which represents both cotyledons tends to lie in a straight 
line with the suspensor and future axis. Thus, when later the 
plumule is developed, it must take up a lateral position (see 60; 
p. 340, fig. 3, Alisma), and only attains its true terminal position 
after germination, when it pushes the cotyledonary member aside. 
Tamus (60, fig. 6) and Commelina, however, are examples in which 
the growing point is terminal and the cotyledon lateral from the 
first. Corydalis cava has a single cotyledon like that of Tamus in 
form and position (60, cf. figs. 4 and 5 with fig. 6); and the simplest 
explanation of both cases is that the single cotyledon represents “the 
fusion of two ancestral cotyledons, but that on account of the early 
formation of the rudimentary plumule, or perhaps because the 
cotyledons have united by one margin only .... the stem-bud has 
never lost its terminal position ” (60, p. 340). 
This view of the monocotyledonous embryo overcomes the 
difficulties of regarding the single cotyledon as a terminal leaf, or as 
in the case of Nelumhium, according to Lyon, as an organ of an 
entirely different nature. 
Miss Sargant’s next point in her very complete and consistent 
theory, is a consideration of the causes and advantages of cotyle- 
