150 Scirgant.— The Reconstruction of a Race of 
of the Dicotyledonous embryo are derived from the single terminal coty- 
ledon of the Primitive Angiosperms by fission. 
Two ways of escape are open. We may accept the possibility of a 
terminal leaf, or we may try to show that the apparently terminal cotyledon 
is derived from a lateral member. 
To begin with the question whether a leaf can be truly terminal. 
Some botanists attempt to solve the problem by saying that the cotyledon 
is an active organ of the embryo and assumes the position best suited to 
its work. That statement is no doubt very true, but it leaves the morpho- 
logical question untouched. When a member assumes new functions, its 
structure is of course modified in the course of generations to suit those 
functions. But modification of a member already fairly well developed 
rarely goes so far that no trace of its original structure remains either in the 
embryonic or the mature condition. If such complete metamorphosis were 
usual, there would be no science of comparative morphology at all. 
When a morphologist says that a leaf is essentially a lateral member, 
he is stating a wide generalization in the form of a law. Experience shows 
that leaves and leaf-like members are arranged laterally on an axis, 
which increases in length by means of a terminal growing-point. The 
rudimentary leaf appears as a lateral out-growth of this terminal meristem. 
This statement is undoubtedly justified as a generalization, for in- 
stances of leaf-like members not clearly lateral in formation are very rare. 
Where an axis is present and the whole of its terminal growing-point is 
converted into a single member, there is a very strong presumption against 
that member as a leaf. The burden of proof rests with those who assert it 
to be so. 
The cotyledon of Alisma, however, hardly comes under this rule. As 
Hanstein pointed out in 1870, neither axis nor growing-point is present 
when it is formed ( 35 , p. 40, pp. 58-61, pp. 90-98). The pro-embryo is 
meristematic throughout, and is undifferentiated except for the external 
distinction between suspensor and embryo proper. The direction of the 
future axis is first indicated by the formation of a plerome cylinder. As 
a rule, no specialized growing-point is formed for some time afterwards. 
The independent results of Hegelmaier ( 36 ) and Fleischer ( 25 ) showed 
in 1874 that the projection of tissue called by Hanstein the stem-apex is in 
some Monocotyledons the first leaf. The second is developed directly from 
a region near the base of the first, the third from the second, and it is some- 
times a long time before a rudiment appears which becomes the apex of a 
true axis. In fact, for some time in such an embryo each successive leaf is 
terminal in the same sense as the cotyledon. When the rudimentary axis 
of such an embryo does appear, it is apparently a lateral outgrowth from 
the base of the last formed leaf. By degrees, as the axis becomes better 
defined, its growing-point assumes a terminal position, and the succeeding 
