i879-] THE GARDENER'S PRIMER. 225 



more species called a genus (or genera, in plural), and each genus not 

 less permanent or distinct than the different species included in it. 



Each genus, in like manner, will be found to have been grouped 

 with other genera, and then placed in a family, as a natural order is 

 called ; and each family in its turn will again have to be arranged 

 into one or other of the following four great classes : First, Dicoty- 

 ledonous plants — that is, plants whose seed is furnished with two 

 cotyledons, or seed-lobes : by far the larger number of species of 

 flowering-plants belong to families of this class, and from the struc- 

 ture of their stems they are also called Exogenous. Second, Mono- 

 cotyledonous plants — that is, plants whose seed is furnished with only 

 one cotyledon, or at least only one is apparent, and from the struc- 

 ture of their stems they are called Endogenous. Third, Polycotyle- 

 donous plants, with three or more cotyledons, of which the family of 

 Coniferae or Eir tribe and Palms are good examples ; and, Fourth, 

 Acotyledonous plants — that is, plants whose seeds or spores have no 

 cotyledons, of which Eerns, Mosses, and Eungi are good examples, 

 and from the structure of their stems they are called Acrogenous. 

 Our remarks are applicable for the most part only to plants belong- 

 ing to the first and second of these great classes. 



Each plant is named with its generic and specific name, generally 

 in Latin or Greek. Many of the specific names have been chosen ac- 

 cording to the characters of parts of the plant, such as the leaf, as 

 serrata, dentata, salicifolia ; or according to their local situations or 

 habitat, such as, arvense, pratense, nemorosum, sylvaticum, aquatica, 

 rupestre, or nivalis; or according to the uses or attributes of the plant, 

 such as somniferum ; or according to its time of flowering, as vernum, 

 cestivum, or autumnalis. 



The origin of species has recently been the subject of much contro- 

 versy, and much time and labour expended to prove that the charac- 

 teristics of species are not of such permanent nature as to be entitled 

 to be regarded as the landmarks in plant classification they have 

 hitherto been. However this may be, it will be well to bear in mind 

 that whatever may be the final result of these inquiries, and which 

 really do no harm, it will be always necessary to make use of specific 

 descriptions of the characteristics of plants in order to render them in- 

 telligible, and to arrive at accurate views of Geographic Botany. 



Each plant has, for the purpose of holding it in its place, and for 

 obtaining nourishment and for storing it up sometimes, as in bien- 

 nial plants, a root or descending axis, or earth end, or alkali ex- 

 tremity, formed at the end of the embryo, but in connection or con- 

 tinuation with the stem, and from which numerous root -fibres, 

 covered with fine hair-like roots — in reality elongations of cells in the 



