CLASSIFICATION OF PLANTS. 9 



20. Plants have been classed according to the Linnean or Artificial System, 

 and according to the Jussieuan or Natural System ; but the latter alone is 

 of any use in a work like the present. By the Natural System plants are 

 thrown into easily recognised groups, bearing a general resemblance, both in 

 exterior appearance and in internal properties, and for the most part also 

 requiring the same kind of culture. Hence we are enabled to speak of 

 plants in masses, which greatly facilitates the discovery and recollection of 

 their names, the acquiring of knowledge respecting them, and the communi- 

 cation of what we know of them to others. 



21. All plants may be divided into three grand classes, founded on their 

 structure. The first class is called Dicotyledoneae, from the seedlings having 

 two or more seed-leaves, and also Exogenae, from the growth being produced 

 from the outside of the stem. The second class is called Monocotyledonae, 

 from the seeds producing only one seed-leaf, and also Endogenae, from the 

 growth being added from the inside of the stems. The third class is called 

 Acotyledoneae, from the seedling plants being without proper seed-leaves; Cel- 

 lulares, from their structure consisting entirely of cellular tissue ; and Aero- 

 gens, signifying increasing by additions to the extremity merely, and not by 

 the formation of new matter internally or externally, throughout their whole 

 length, as in endogens and exogens. We shall use only the terms Exogens, 

 Endogens, and Acrogens. 



22. Exogens are flowering plants, vascular in their structure, furnished 

 with woody fibre and spiral vessels ; with stems mostly having distinct layers 

 of wood and bark, and having pith ; the leaves being with branching lateral 

 veins, and the seeds with two or more cotyledons. By far the greater num- 

 ber of European plants belong to this class, which is readily known, even 

 when a fragment of a leaf or a stem is obtained, by the reticulated venation 

 of the former, and the concentric circles of the latter. 



23. Endogens are flowering plants with a vascular structure, furnished 

 with spiral vessels, and imperfectly formed woody fibre j they have leaves 

 with longitudinal or parallel veins, but never reticulated ; and seeds with 

 one cotyledon only, or if two, they are not placed opposite and even with 

 each other, as in exogens, but one of them is placed at the side of the other 

 in the disposition which botanists call alternate. This class includes all the 

 immense order of grasses, and also hyacinths, tulips, narcissi, crocuses, irises, 

 and most bulbs ; the well-known yucca or Adam's needle, and all palms. 

 From a single fragment of the stem or leaf of an endogen, the class to which 

 it belongs can be recognised with as great ease as in the case of exogens. 



24. Acrogens are flowerless plants with a cellular structure, consisting 

 either of cellular tissue alone, as in lichens and mosses, or with tissue and 

 some few imperfect vessels, as in ferns. They grow by additions to the 

 upper extremity only, as the name implies. Their seed is produced without 

 apparent flowers ; it is not furnished with cotyledons, and it grows from any 

 part of the surface of the plant ; on the under side of the leaf, as in most 

 ferns, on the edges of the foliaceous thallus of lichens, and from the extre- 

 mities on the sides of mosses. This class of plants is easily recognised by 

 the general observer ; lichens, mosses, and fungi, being universal, and ferns 

 frequent and readily recognised by the markings on the backs of their leaves. 



25. Of these three classes of plants, the exogens are unquestionably the 

 highest in the scale of organisation even to the general observer. The leaves 

 of the endogens, at least of temperate climates, are almost all simple, and 

 have little or no variety in their venation or margins. Those of the mime- 



