328 BOTANICAL GAZETTE [MAY 
bers differentiated from the mass of meristem which constitutes 
the embryo. Among monocotyledons the single cotyledon 
forms a club-shaped termination to the axis, and the boundary 
between these members is first clearly defined by the appearance 
of a lateral cleft within which is formed the growing-point of the 
stem. Thus the cotyledon is apparently terminal in monocoty- 
ledons, the stem bud lateral (fig. 3 on p. 340). 
In the dicotyledonous embryo a similar enlargement appears 
at one end, but it is sooner or later divided into two lobes by a 
median cleft, within which the stem bud is formed. As soon as 
this takes place the cotyledons appear Jateral, the stem bud 
terminal. 
The accepted interpretation of these facts is that the club- 
shaped enlargement of the dicotyledonous embryo before lobing 
begins is equivalent to that which gives rise to the single seed 
leaf of monocotyledons. Its subsequent bifurcation indicates 
the origin of both cotyledons from that of an ancestor which 
possessed but one. This interpretation has been recently urged 
by Mr. Lyon in his paper on Nelumbium.t In this species the 
meristematic mass at the end of the embryo attains some size 
before it gives rise to a pair of cotyledons. The stem bud first 
appears in a lateral position with regard to it, and later reaches 
a symmetrical station between the cotyledons by degrees. The 
embryo is said by Mr. Lyon to pass through a monocotyledonous 
stage, and he is even prepared on the strength of these observa- 
tions to class Nelumbium among monocotyledons. Professor 
Strasburgers has observed with great force that the position of 
the embryo at one side of the embryo sac of Nelumbium has 
probably more to do with its one-sided development than any 
ancestral reminiscence. 
A. similar criticism may, I think, be applied to the whole 
argument. A parasitic mass of meristem which is forced to 
develop within very narrow limits naturally assumes the most 
convenient form, and any detail of shape is at least as likely to 
be due to its environment as to inheritance from remote ancestors. 
*Lyon, H. L., Embryogeny of Nelumbo. Minnesota Bot. Studies 2 : 643. 1901- 
5 STRASBURGER, E., = Pe, zur Kenntniss von Ceratophyllum submersum- 
Jahrb. Wiss. Bot. 37 : 477. 
