THE CLASSES OF PLANTS. 3 



Beyond Thallogens arc found multitudes of species, which like the former 

 are not furnished by natm-e -with flowers, but which otherwise approach 

 closely to the higher forms of structure, occasionally acquiring the statm-e of 

 lofty trees. They have breathing-pores in their skin ; their leaves and 

 stem are distinctly separated ; in some of them, those spiral threads which 

 form so striking a portion of the interna], anatomy of a more perfect species, 

 exist in considerable abundance ; and finally, they multiply by reproductive 

 spheroids, or spores, either formed without the agency of sexes, or, if the 

 contrary shall be proved, at all events not possessing bodies constructed like 

 stamens on the one hand and embryos on the other. Theii- stem, however, 

 does not increase in diameter ; it only grows at the end, and hence it has 

 given to such plants the name of Acrogens.* 



The changes which thus occur in the races of Thallogens and Acrogens, 

 represent the progress of development in the remainder of the Vegetable 

 Kingdom. A sphere, called a pollen grain, protrudes a tube into a soft pulpy 

 receptacle in the interior of an o\"ide ; there the new plant takes its birth, at 

 first in the form of a cell, which by degrees forms a thread (the suspensor), 

 then generates a cellular mass (the young embryo), and eventually becomes a 

 mass of cells arranged in the form of stem and leaves (the perfect embryo, 

 with its cotyledons, radicle, and plumula). But this is not the end of growth ; 

 it is rather the beginning. A loftier destiny awaits such plants ; flowers are 

 to be formed, seeds to be fertihsed, and this is to be efi'ected by a complex 

 apparatus unknown in Acrogens or Thallogens. 



Foremost among the more perfect races comes a most anomalous collec- 

 tion of species, called Rhizogens, or Ehizantl>s. These plants, leafless 

 and parasitical, have the loose cellular organisation of Fungi ; a spiral struc- 

 tm-e is usually to be found among their tissue only in traces. Some of them 

 spring visibh' from a shaj^eless cellular mass which stands in place of stem 

 and root, and seems to be altogether analogous to the thallus of Fungi ; and 

 it is probable, that they all partake in this singular mode of growth. Their 

 flowers are like those of more perfect plants ; their sexual apparatus is com- 

 plete ; but their embryo, which is not fiu-nished with any visible radicle or 

 cotyledons, appears to be a spherical or oblong homogeneous mass. Khizogens 

 seem, in fact, of an intermediate nature between Fungal Thallogens and 

 Endogens. 



The remainder of the Vegetable Kingdom consists of plants having flowers, 

 and propagated by seeds ; that is to say, by bodies procreated by the mutual 

 action of two manifest and undoubted sexes. Such plants are therefore 

 called Phsenogamous or Sexual. 



Sexual plants are themselves divisible into two unequal masses. Of 

 these masses one consists of sjDecies whose germination is endorhizal, whose 

 • embryo has but one cotyledon, whose leaves have parallel veins, and whose 

 trunk is fomied of bundles of spiral and dotted vessels guarded by woody 

 tubes ; which bundles are arranged in a confused manner, and are reproduced 

 in the centre of the trunk. These are Endogens. 



The other mass is composed of innumerable races having an exorhizal 

 geimination, an embryo with two or more cotyledons, leaves having a net- 

 w^ork of veins, and a trunk consisting of woody bundles composed of dotted 

 and woody tubes, or of woody tubes alone, arranged around a central pith, 

 and either in concentric rings, or in a homogeneous mass, but always having 

 meduUary plates, forming rays from the centre to the circmnference, and 



* Thallogens and Acrogens together constitute the Acotyledones of Jussieu, the Exembryonata: 

 or Arhiz^ of Richard, the Agam^, Cryptogams, or ^theogams oi others, the Nemea of i^'ries. 



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