320 IMPERFECTIONS OP THE LINNJSAN SYSTEM. 



student meet with a specimen which has five, six, or ten stamens, 

 he will vainly search for its character among the genera of the 

 Linnaean class to which it would seem to belong ; and unless he 

 happen to consult a book which makes special mention of the 

 genus in these several classes, he will be altogether at fault. 

 Suppose that some more knowing Botanist tells him that his 

 plant is a Polygonum, he will again turn to his book, wondering 

 how he could have overlooked it ; but he will find the genus in 

 the class Octandria, in spite of the different number of stamens 

 in the specimen before him : and he will then learn that it is 

 placed in the genus Polygonum on account of its strong general 

 resemblance to other Polygonums, although differing from them 

 in characters which are ordinarily considered as sufficient to esta- 

 blish classes and orders. Again, the greater part of the species 

 of the genus Rhamnus (Buckthorn) possess both stamens and 

 pistils in the same flower ; but the species most commonly known 

 in this country on account of its purgative properties is Dioecious, 

 the staminiferous flowers being on one plant, and the pistilliferous 

 on another (. 435). The student who meets with it, therefore, 

 would seek for it in the class Dicecia, where he would be disap- 

 pointed as before ; since, as in most species the flowers are com- 

 plete, it is placed in the class and order to which the number of 

 its stamens and pistils would refer it. 



482. Such exceptional cases occur much more frequently than 

 is commonly supposed. It has been proved that, in fourteen 

 divisions of the Linnaean system, including 173 British genera, 

 there are no less than 43 exceptions, one-quarter of the whole; 

 and that out of 274 genera of North America, belonging to 

 eighteen Linnaean sections, there are 78 exceptions, rather more 

 than a quarter. These facts are important, both as preparing 

 the student to meet with such difficulties, even in the study of 

 the Linnaean system, which is generally considered so easy of 

 application ; and also as showing the imperfection of the system 

 itself, which is of no value whatever, beyond the temporary pur- 

 pose of facilitating the early studies of the Botanical Student. 

 In well-arranged descriptions of British Plants (such as Hooker's 

 British Flora, which may be strongly recommended for this pur- 

 pose) the most perplexing of these cases are noticed, in such a 



