TO BOTANY. , 105 



serving that it wanted the nectariferous pore ; and 

 Aloe and Agave had been blended, till it was ob- 

 served that in the latter the stamina were inserted in 

 the corolla, and not in the receptacle. 



When the characteristic mark of any genus is ob- 

 served in some species of another genus next of kin 

 to it, a like caution is again necessary on the other 

 hand; lest we should multiply the genera by parting 

 species that should stand together:- Thus we find, 

 that in Sedum, Sempervivum, Rhodiola, Crassula, 

 Tillaea, and Cotyledon, the nectaria adhere to the 

 base of the pistillum ; in Epilobium and Oenothera, 

 the calyx is tubulose ; in Mespilus, Crataegus, and 

 Sorbus, the structure of the flower is alike ; and in 

 both Alnus and Betula, there are three florets on the 

 foliole of the amentum*. 



CHAP. XXX. 



By WHAT PARTS OF FRUCTIFICATION THE GENUS 



MAY WITH THE MOST CERTAINTY BE DE- 

 TERMINED. 



THE more constant any part of the fructification 

 is found, through the several species of any genus, 

 the more it may be relied on with certainty as a 

 characteristic mark of that genus : thus in Hypecoum 

 the nectarium is constant, but not the siliqua ; the 

 Convallaria is constant in the spotted berry, but not 

 in its corolla ; the Lobelia in its corolla, but not in 

 its fruit; the Cassia irt its corolla, but not in its si- 

 liqua ; and the Verbena in its calyx and corolla, but 

 not in its stamina and seeds. 



* The Alnus and Betula are joined by -Linnaeus under the 

 title of Betula. The rest of these instances he has kept se- 

 parate, notwithstanding the doubt raised here concerning the 

 propriety of distinguishing them. 



