INTRODUCTION. 27 
such secondary points as the structure of the carpels. In the 
lines laid down above it will be seen that the nature of the seed 
is considered to be of prime morphological importance. This 
view, I am inclined to think, will repay study, for it serves to 
clear away some mists which should have been dispelled long 
ago, had it not happened that ancient terminalogies and 
conservative taxonomies stood directly athwart the light. 
Subdivisions of the Metaspermae. The recent researches of 
Treub (40) have made necessary a new subdivision of the 
Metaspermae more fundamental than that into the Monocoty- 
ledones and Dicotyledones. Upon examination of members of 
that peculiar Australasian genus, Casuarina, it was found that, 
unlike any other known Metaspermae, they were devoid of 
micropylar canals, and that the mature ovules split along the 
chalazal line and through this cleft the pollen-tube was permit- 
ted toenter. Itis then proposed by Treub to divide Metaspermae 
into two divisions, separating the more Selaginella-like Casuar- 
inaceae from the rest under the name of Chalazagameae. Plants 
of this division are comprised under the single rather small 
genus, Casuarina. All the rest of the Metaspermae unite, so 
far as known, in having a particular opening, the micropylar 
canal, penetrating the ovular membranes and permitting the 
end of the pollen-tube to be appressed against the embryo-sac 
(megaspore) in which the two eggs are developed which 
produce respectively the endosperm and embryo of the seed. 
This division is termed by Treub, Porogameae. 
The Porogameae are divided into the Monocotyledones and 
Dicotyledones. In the first division the embryo undergoes a 
distinct type of segmentation-stages (41) and in most cases 
developes the apical meristem from two initials instead of from 
three (42). Moreover there is but one cotyledonary leaf 
developed. 
In the Dicotyledones there are commonly three initials for the 
apical meristem, so that the plerome, dermatogen and periblem 
layers has each its own mother-cell. The segmentation stages 
are peculiar and moreover there are two cotyledonary leaves 
developed. 
The Monocotyledones do not admit of further subdivisions of 
higher grade than the orders, as described and limited well by 
(40). Treub: Ann. Jard. Buitenz. X. 145-231 (1891). 
(41. Hanstein: Hntwickelung des Keimes der Monokotylen und Dikotylen. pp. 1—1125 
taf. 1-18 (1870). 
(42), Wan Tieghem and Douliot: Recherch Comp. Endogen. Member. Ann. Sci. Nat. 
Botan., 7, VIII, 1 (1888), and Douliot Ul. c. 7, XI, 283 (1891). 
