INTRODUCTION. 
497 
rays so as to form a perfect ring (the cambium-ring), and then produces regularly new 
layers of phloem on the outside and of xylem on the inside. In the primary roots and 
the stouter lateral roots of Gymnosperms and Dicotyledons an increase of thickness 
also takes place by the subsequent formation of a closed cambium-ring, which, like that 
of the stem, is not found in Cryptogams, and commonly leads to the formation of strong 
persistent root-systems, which are more often replaced physiologically in Monocoty- 
ledons by rhizomes, tubers, and bulbs. With the persistent increase in thickness is 
connected, finally, the active and extensive production of cork, a process foreign both 
to Cryptogams and to Monocotyledons. It will be more convenient, however, to defer 
the special discussion of these points also until we are treating of the characteristics of 
the separate classes. 
SYSTEMATIC REVIEW OF PHANEROGAMS. 
The distinguishing characteristic of Phanerogams, as contrasted with Cryptogams, 
lies in the formation of the Seed. This organ is developed from the ovule, which, in 
its essential part the nucellus, produces the Embryo-sac, and in this the Endosperm and 
the Oosphere. The latter is fertilised by the Pollen-tube, an outgrowth of the Pollen- 
grain, and, after, produces the Embryo borne on a Suspensor. The phanerogamic 
plant which is differentiated into Stem, Leaves, Roots, and Hairs, corresponds to the 
spore-forming (asexual) (Sporophore) generation of Vascular Cryptogams ; the Embryo- 
sac to the Macrospore ; the Pollen-grain to the Microspore ; the Endosperm is equivalent 
to the female ProthaUium ; and the Seed unites in itself, at least for a time, the two 
generations, the ProthaUium (Endosperm), together with the young plant of the second 
generation, the Embryo. 
Flowering Plants may be classified as follows : — 
I. Phanerogams without an Ovary. 
The ovules are not enclosed before fertilisation in a structure (the Ovary) resulting 
from a cohesion of carpellary leaves. The endosperm arises before fertilisation, and 
forms archegonia {i.e. ' corpuscula '), in which the oospheres originate. The contents 
of the pollen-grains are divided before the formation of the pollen-tube, corresponding 
to divisions taking place in the microspores of Selaginella. 
I. Gymnosperms. The first leaves produced from the embryo are arranged 
in whorls of two or more. 
A. Cycadece. Branching of the stem very rare, or entirely suppressed ; 
leaves large, branched. 
B. Con'iferce. Axillary branching copious, but not from all the leaf-axils ; 
leaves small, not branched. 
C. Gnetacece. Mode of growth very various ; flowers similar in many 
respects to those of Angiosperms. 
II. Phanerogams with an Ovary.. 
The ovules are produced in the interior of a structure (the Ovary) formed by the 
cohesion of carpellary leaves (often only of one carpel, the margins of which have 
become coherent), bearing at its summit the stigma upon which the pollen-grains 
germinate. The endosperm is formed after fertilisation at the same time as the 
embryo, both remaining rudimentary in some cases. A division of the contents of the 
pollen-grain is indicated. The branching is almost always axillary and from the axils of 
all the foliage-leaves. 
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