3H COMBINATION OF SPECIES INTO GENERA. 



which are probably reducible to 6 or 8. These details are here 

 introduced, for the purpose of putting the young Botanist on 

 his guard, against the tendency to multiply species, which is now 

 prevalent among superficial writers, and which is still further 

 encouraged by Gardeners, who give new specific names to such 

 varieties as those just alluded to, and even to hybrids between 

 these (. 454). 



477. When the Botanist has satisfied himself regarding the 

 species which he has collected, his next step is to combine those 

 amongst which he finds the greatest resemblance, into genera. 

 Now in this process he must not be altogether influenced by simi- 

 larity in their general external aspect ; for this will often con- 

 ceal great differences in their most important organs. There 

 are certain parts which furnish essential characters, without 

 similarity in which it would be wrong to associate species, how- 

 ever alike in other respects, in the same genus ; and, on the 

 other hand, there are parts so susceptible of variation, that the 

 differences between them must be very striking indeed, to war- 

 rant the plants being arranged under different genera, when they 

 agree in what have been termed the essential characters. Thus, 

 for instance, the general outline of the leaf has been stated to be 

 often subject to great variety, in accordance with the degree in 

 which the space between the veins is filled up with fleshy 

 parenchyma (. 234, 5); and in most cases, a difference in the 

 outline of the leaves of two plants, the distribution of the veins 

 remaining the same, would not alone serve to cause two plants 

 exhibiting it to rank even as distinct species. But any consider- 

 able alteration of the veining would be held sufficient for such a 

 separation ; though the two plants, if agreeing in the structure 

 of their organs of fructification, would still be placed in the 

 same genus. On the other hand, a marked and constant dif- 

 ference in the organs of fructification would be rightly held 

 sufficient to place the two species in different genera, even though 

 the form and veining of the leaves might be precisely the same, 

 On the relative value of the characters furnished by the different 

 organs more will hereafter be stated. 



478. Even when thus grouped together into genera, however, 



