NATURAL SYSTEMS OF CLASSIFICATION. 409 



classification, while those of fructification would furnish many ; 

 and such is the fact. Hence it is that the great classes of 

 plants are principally distinguished by their organs of growth, 

 and that in the numerous minor groups such peculiarities are 

 comparatively disregarded, their chief distinctions being derived 

 from their parts of reproduction." 



Taking these principles as our guide, we should regard the 

 structure of the embryo as of the first importance, as it contains 

 within itself in a rudimentary condition all the essential organs 

 of a plant. Hence, according to its presence or absence, we 

 divide plants into two great divisions, called Cotyledonous and 

 Acotyledonous ; the fomier being propagated by true seeds, in 

 which the embryo possesses one or more cotyledons, a radicle, 

 and a plumule; while the latter are propagated by spores, in 

 which we can discover no such distinction of parts. As Coty- 

 ledonous Plants vary in the number of their cotyledons, these 

 may be again divided into two classes — those possessing one 

 cotyledon being called Monocotyledonous, those with two 

 Dicotyledonous. 



Next in value to the embryo, is tlie growth and internal struc- 

 ture of the axis. Thus, the mode in which the root is produced, 

 furnishes us with three characters, called respectively, Hetero- 

 rhizal, Endorhizal, and Exorhizal. The growth and internal 

 structure of the stem also supplies us with three characters, 

 called Acrogenous, Endogenous, and Exogenous ; while those 

 plants which have no stem, are termed Thallogenous. 



Next to the axis we place the leaf, which, as regards vena- 

 tion, presents three distinctive characters; thus, in Acrogenous 

 Plants the leaves or fronds have commonly a forked venation ; 

 those of Endogenous Plants are parallel-veined ; while those of 

 Exogenous Plants are net-veined or reticulated. Again, stem- 

 less plants have no true leaves, but produce a flattened cellular 

 expansion or thallus, which is veinless. 



If we now proceed to the organs of reproduction, we find that 

 while some plants have flowers with evident sexes, others have 

 no flowers, and their sexual organs are more or less concealed ; 

 hence the former are called Phanerogamous or Phgenogamous, 

 the latter Cryptogamous. The andrcecium and gyncecium are 

 of the first importance amongst the reproductive organs, because 

 they are essential to the formation of the seed of flowering plants; 

 while the antheridia and archegonia may be considered as 

 possessing about the same importance among flowerless plants. 

 Next in order comes the fruit; thus the presence of a true 

 pericarp is the main characteristic of Angiospermous, and its 

 absence that of Gymnospermous Plants. 



Next to the fruit must be placed the floral envelopes, which, 

 as regards the number of their parts, are usually ternary 

 in Monocotyledonous Plants, and quinary or quaternary in 



