BRITISH ALG.E. 



CLASSIFICATION. 



IN the earlier days of systematic botany the plants which 

 we now know under the common term Alga, formed, with 

 the Lichens, a single order of the class CRYPTOGAMIA in the 

 Linnaean system, and a single order of the ACOTYLEDONOUS 

 plants in the Jussieuian. As these vegetables became better 

 known to botanists, differences in structure were noticed be- 

 tween the aerial Algae or Lichens, and the submerged, or 

 true Algae, and these differences led to the establishment and 

 general recognition of two groups, which were supposed to 

 be equivalent to what are called NATURAL ORDERS in our 

 modern system. 



This separation into two orders was a great improvement 

 in classification, but it has not been found to be sufficient. 

 Ill every system it is desirable that the same word should 

 express the same value : thus, that the species associated to- 

 gether into an order in one part of the system should be as 

 closely related in character to each other as those which 

 comprise an order in another part of the system. 



Applying this rule to the orders of flowering and of flower- 

 less plants, it is obvious that the orders of the former group 

 are defined by characters far more exact ; and that each ge- 

 nus included io one of the orders has a much closer connex- 

 ion with its neighbour (or co-ordinal) than exists among the 

 genera of such cryptogamic "orders" (we should rather call 

 them disorders] as Algae, Lichens or Fungi. 



To confine ourselves to the Algae : the differences between 

 the less developed members and the most perfect kinds of 

 these plants are fully as great, perhaps greater, than are to 

 be found between the least and most perfect individuals of 

 either of the great groups EXOGENS and ENDOGENS. So that 

 it is no longer possible to assign the term NATURAL ORDER 

 to a group of such extent, comprising structures so dissimilar 

 one from another. 



