58 Mr. W. 8. Macl£a v on certain general Laws regulating 



In the first place, M. Fries lays it down as a rule, which is 

 quoted above, that he admits no groups whatever to be natural 

 unless they form circles more or less complete. Let u# then 

 apply this rule to what he terms his central group, and which 

 he makes always to consist of two. Does this form a circle ? If 

 not, the group cannot be natural according to his own definition. 



If, on the other hand, its two component groups are each 

 circles, then these are natural. Thus the Ftilota will not form 

 one circle, but two ; consequently they form two natural groups, 

 which is furthermore proved by their parallel relations of ana- 

 logy. If we turn to Fungi also, the Ilymenini, according to 

 M. Fries, do not form one circle, but two ; one of Pileati, the 

 other of Clavati ; so that instead of the Hymenomycetes forming 

 four natural groups, viz. Sclerotiacei, Tremellini, Uterini, and 

 Hymenini, they form, if our author be correct, five ; viz. Scle- 

 rotiacei, Tremellini* , Uterini, Pileati, and Clavati. 

 ■' But, to understand this still better, we had as well perhaps 

 enter a little deeper into our author's theory. Every group, he 

 says, which expresses well the character of the superior group 

 to which it belongs, is called the centrum ; by this, not meaning 

 the centre of a circle, but the site of the normal form or perfec- 

 tion of the particular structure common to the superior group, of 

 which it forms a part. The word perfection, even as here used, 

 requires explanation ; for it does not, as might be supposed, in 

 this place signify affinity to any particular group. Our author, 

 on the contrary, most properly says, that the idea of perfection 

 in structure has nothing to do with affinity t. " Ipsa haec affini- 



tas 



* This appears to be one of those interesting groups which connect tlie least per- 

 fectly organized beings with those which are the most perfectly organized. In the de- 

 partment of Hysterophyta it is to the Coniomycetes or lowest Fungi, what in the animal 

 kingdom the Fermes are to tlie Acrita. 



t To the general observations on this subject,- as connected with the animal king- 

 dom. 



