410 SYSTEMATIC BOTANY. 



Dicotyledons. Lindley remarks, that "the floral envelopes seem, 

 to be unconnected with functions of a high order, and to be 

 designed rather for the decoration of plants, or for the purpose 

 of giving variety, to the aspect of the A^egetable world ; and, conse- 

 quently, their number, form, and condition, presence or absence, 

 regularity or irregularity, are of low and doubtful value, except 

 for specific distinction. There seems, indeed, reason to expect 

 that every natural order will, sooner or later, be found to con- 

 tain within itself all the variations above alluded to," 



The presence or absence of bracts, as well as their appearance 

 and general arrangement ; and the characters derived from the 

 different modes of inflorescence, are even of less value than those 

 of the floral envelopes, and must be considered, therefore, as 

 occupying the lowest place in our series of the relative value of 

 characters furnished by the organs of plants. 



Such are the general principles which must be attended to by 

 those who desire to arrange plants according to their natural 

 affinities, and those systems of classification will be most natural 

 in which the organs of the highest value, and those least liable 

 to change, are especially relied on, in the determination of the 

 affinities of plants. It must be borne in mind, however, that in 

 the best devised natural systems there must be (at least at pre- 

 sent) much that is artificial, so tliat all that we mean by the 

 Natural System is, that it expresses, as far as is possible only, the 

 arrangement of plants according to their natural affinities. (See 

 p. 397.) This imperfection of our natural systems necessarily 

 arises from our incomplete knowledge of existing plants ; for as 

 our acquaintance with new kinds is becoming every day extended, 

 our views are liable to be modified or changed, and even supposing 

 plants be ever so naturally arranged, we should be still unable 

 to place them in a linear series, for "Different groups touch each 

 other at several different points, and must be considered as al- 

 liances connected with certain great centres. We find also that 

 it is by no means easy to fix the limits of groups. There are 

 constantly aberrant orders, genera, and species, which form links 

 between the groups, and occupy a sort of intermediate territory. 

 In this, as in all departments of natural science, there are no 

 sudden and abrupt changes, but a gradual transition from one 

 series to another. Hence exact and rigid definitions cannot be 

 carried out. In every natural system there must be a certain 

 latitude given to the characters of the groups, and allowances 

 must be made for constant anomalies, in as far as man's defi- 

 nitions are concerned." 



Natural Systems. — We now proceed to give an abstract of 

 the more important natural systems. The first attempt at 

 arranging plants according to their natural affinities was by 

 our celebrated countryman, John Eay, in the year 1682 ; and 



