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 to enter. It is then proposed by Treub to divide Metaspermae 

 into two divisions, separating the more Selaginella-like Gasuar- 

 inaceae from the rest under the name of Ghalazagameae. 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 Monocoty led ones 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. Baitenz. X. 145-231(1891). 



(41',. Hanstein: Entwickelung des Keimes der Monokotylen und Dikotylen. pp. 1 M2 

 taf. 1-13 (1870). 



(42), Van Tieghem and Douliot: Recherch Comp. Endogen. Member. Ann. Sci. Nat. 

 Botan., 7, VIII, 1 (1888), and Douliot I. c. 7, XI, 283 (1891). 



