180^ Mr. Roscoe on Artificial and Naiural 



purpose for which they were intended in the preceding volume, 

 as the quantities 2},q,p',q' give now the relative position of 

 the moon to the stars and the motion of the former, they have, 

 notwithstanding, been added, in order to facilitate the calcu- 

 lation of the occultations of such stars as are not given in our 

 list. 



Both my own comparison and the communications of others 

 have brought to my knowledge a greater number of misprints 

 than ought to exist in such a volume. Most of them, or almost 

 all, do not arise from a want of attention in the printing-office, 

 which has perfectly fulfilled every expectation, but from the 

 unavoidable transferring and copying of the columns. It would 

 hardlv be worth while to enumerate them, as by the regularity 

 of the differences every considerable error will be easily de- 

 tected at first sight. I beg, however, to add this one remark — 

 that, as in the case of logarithmic tables one acquires the habit, 

 when taking out a number, always to cast one's eye on the 

 preceding and following number, so, in the use of this book, 

 the small trouble of slightly looking at the numbers close to 

 the one wanted, ought not be dispensed with. For accurate 

 calculations it is besides always necessary to form several or- 

 ders of differences. 



XXV. On Artijicial and Natural Arrangements of Plants : atid 

 particularlij on the Systems of Linncvus and Jussieu. By 

 William Roscoe, Esq. F.L.S. 



[Concluded from page lO-I.] 

 A CCORDING to each of these systems, the classes are 

 -^^ divided into orders. Linnaeus, still aiming at simplicity, 

 but founding his decisions on strong natural distinctions, has 

 for this purpose recourse to the pistillum, or style, the imme- 

 diate organ of impregnation, and essential to the formation of 

 the fruit. As a single word has expressed the class, so an- 

 other word now gives us the order ; and to a practical bo- 

 tanist the expression Pentandria monogynia suggests the idea 

 of a division of plants including, among many others, the 

 natural order of asperifolia?; as that oi Pentandria digynia 

 does of the umbellifer.Te. The difficulties under which Jussieu 

 labours now become apparent. He has indeed formed the 

 vegetable kingdom into fifteen classes; under which heads he 

 has arranged one hundred tribes or orders, each consisting of 

 various families of plants supposed to be allied to each other; 

 but when we ask for the distinctions of these orders, or, in 

 other words, by what peculiarities they are to be recognised, 



and 



