418 SYSTEMATIC BOTANY, OR 



Monocotyledonous Plants, and quinary or quarternary in 

 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 vegetable 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 

 afiinities, 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 

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

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

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

 an-angement of plants according to their natural affinities. (See 

 p. 406.) This imperfection of our natural systems necessarily 

 arises from our incomplete knowledge of existing plants, foras 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, Ave should be still unable 

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

 other at several different points, and must be consideredas alliances 

 connected with certain great centres. We find also that it is by 

 no means easy to fix the limits of groups. There are constantly 

 abcn-ant 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 tlic characters of the groups, and allowances must be 

 made for constant anomaUcs, in as far as man's definitions arc 

 concerned." 



Natdral Systems. — Wc now ])roceed to give an abstract of 

 the more important natural systems. The first attempt at 

 arranging phvuts according to their natural affinities was by 



