Modern Systems of Classification. 209 
we venture to differ on a point of detail from all three of the 
authorities named. We refer to the position accorded to the order 
Verticillatae. It will be remembered that Casuarina —the only 
genus of the order—was regarded by Eichler 1 as probably best 
placed in his order Amentaceae ; and it was once so placed by 
Engler 2 himself. It was removed from this position after the 
account by Treub 3 of the processes that went on in the ovule ; and 
it is now usual (though, we believe, quite erroneous) to place the 
Verticillatae as the first, and presumably the most primitive order 
of Dicotyledons. Warming justifies this position of the order is 
the following words (p. 167):—“ By the transfusion tissue, by the 
type of stomata, and especially the ovular peculiarities, this order 
seems to be related with the Gymnospermae, especially the Gnetales.” 
The ovular peculiarities are thus summarised:—“ In the nucellus, 
which has two integuments, many embryo-sacs are formed, of which 
only one is fertilised. The egg-apparatus consists, as among 
Angiosperms, of an egg-cell and two synergidae ; but antipodal cells 
are not formed. Before fertilisation, a prothallus of many free 
nuclei is formed, which after fertilisation becomes a nutritive tissue. 
The fertilisation is chalazogamic.” These remarks are based on 
the work of Treub ( loc. cit.). Treub’s observations, however, have 
been shown by Frye 4 to be inaccurate in a few particulars, such as 
the possession of an anomalous embryo-sac. All the other characters 
described by Treub as occurring in Casuarina have been found in 
Carpinus, and many of them in Corylus, Betula, and Alnus. The 
characters here referred to are the occurrence of chalazogamy, the 
occurrence of more than one embryo-sac (numerous embryo-sacs 
occurring in Carpinus ), the formation of a caecum from the originally 
isodiametrical embryo-sac, the occurrence of tracheids among the 
embryo-sacs, the entry of the pollen-tube at the base of the caecum 
in Corylus and Carpinus, the closure of the micropyle, and the fusion 
of the ovule with the wall of the ovary. It has also been shown 5 
that in the type of inflorescence, regarded as a modification of 
Eichler’s type-diagram of the group, the cone-like structure of the 
amentum is not unlike that of Alnus; and the bacterial tubercles 
on the roots of both genera may be instanced as a common biological 
feature. The typical Angiospermous embryo-sac observed by Frye 
(loc. cit.) and the carpellary investment round the ovule described 
by Treub show that the genus should not be separated from the 
Angiosperms, as Treub suggested it should be; and the results 
obtained by Benson (loc. cit.) prove decisively that the position 
accorded to Casuarina by Eichler was a very reasonable one. 
There remain the vegetative characters of Casuarina— the switch¬ 
like habit, the specialised phyllotaxy, the transfusion tissue, and the 
type of stomata—to consider; and we suggest that these are merely 
biological adaptations to the dry climate which species of Casuarina 
affect. On this view, the points of real similarity between Casuarina 
1 “ Syllabus der Vorlesungen ” ; 5 Auflage ; 1890. 
2 “ Pflanzenfamilien,” III, Pt. 1, p. 16; 1889. 
s Ann.Jard. Bot. Buitenz., X, p. 145 ; 1891. 
< Bot. Gaz., XXXVI, p. 101 ; 1903. 
1 See especially Benson, Sunday, and Berridge : “ Contributions 
to the Embryology of the Amentiferse: Part II, Carpinus 
Betulus ” ; in Trans. Linn. Soc., VII, Pt. 3, 1906. 
