;:: PHANEROGAMS. 



outer layers of the stem when this has continued to increase in thickness, outside the 

 foliar bundles (as in Menispermaccce, Aloineae, and Dracaena). 



The further development of the foliar bundles varies in Monocotyledons on the one 

 hand and in Gymnosperms and Dicotyledons on the other hand. In the former they are 

 closed ; in the latter a layer of formative cambium remains, which, in stems that increase 

 rapidly in thickness and become woody, usually prolongs itself across the medullary 

 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. 



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 nucleus, produces the Embryo-sac, and in this the Endosperm and 

 the Embryonic Vesicle. The latter is fertilised by the Pollen-tube, an outgrowth of the 

 Pollen-grain, and, after first growing into a Pro-embryo, produces the Embryo. The 

 phanerogamic plant which is differentiated into Stem, Leaves, Roots, and Hairs, 

 corresponds to the spore-forming (asexual) generation of Vascular Cryptogams; the 

 Embryo-sac to the Macrospore ; the Pollen-grain to the Microspore ; the Endosperm 

 is equivalent to the female Prothallium ; and the Seed unites in itself, at least for a 

 time, the two generations, the Prothallium (Endosperm), together with the young 

 plant of the second (sexual) generation (the Embryo). 



Flowering Plants may be first of all 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 (/. e, ' corpuscula '), in which the embryonic vesicles originate. The 

 contents of the pollen-grains are divided before the formation of the pollen-tube, 

 corresponding to the formation of the microspores of Selaginella. 



Glass XI. Gynmosperms. The first leaves produced from the embryo are 

 arranged in whorls of two or more. 



A. CycadecB. Branching of the stem very rare, or entirely suppressed ; 



leaves large, branched. 



B. ConifercB. 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 



