162 AN INTRODUCTION 



being acquainted with this part. They are found on 

 the serratures at the base of the leaves in Heliocar- 

 pus, Salix, and Amygdalus; on the back of the 

 leaves in Padus, Urena, and Passiflora; and on 

 the Aculei in Bauhinea aculeata, where by the apex 

 of the Aculei a liquor is secreted. The Amygdalus 

 is distinguished from Persica only by the glandules 

 of the serratures ; nor could the species of Urena 

 be ever fixed without examining the glandules of the 

 leaves. The Convolvulus with a tuberculate calyx, 

 is so variable in the shape of its leaves, that it seems 

 divisible into many species, yet is kept together by 

 the glandules ; and there is a species of Monarda, 

 distinguishable from its congeners by the glandules 

 that are sprinkled over the corolla. 



Stipulae are of great consequence in many exten- 

 sive genera, where the species are liable to confusion. 

 Thus in one species of Melianthus the stipulae are 

 solitary; in the other they are in pairs ; and the Cassia 

 auriculata is rendered distinct from all its congeners 

 by the shape of its Stipulae, which are renifonn and 

 barbate. 



HYBERNACLES afford likewise a certain specific 

 difference. 



That Gems or buds often differ greatly in the same 

 genus is proved by Rhamnus ; in which the various 

 species, viz. Cervispina, Alaternus, Paliurus, and 

 Frangula, have all a difference in their buds'; and 

 in that extensive and intricate genus the Salix, the 

 species are, by the structure and foliation of the 

 buds, distinguished with ^reat certainty. 



Bulbs also distinguish the species, as is proved by 

 Scilla, where they afford a real, and almost the only 

 distinction ; and by their situation in the axillae of 

 the leaves, they determine Dentaria, Lilium, Orni- 

 thogalum, Saxifraga and Bistorta. 



INFLORESCENCE affords the truest, and in most 

 genera the most elegant distinction. Thus in Spiraea, 



