SPECIES OF CASSIA WHICH YIELD SENNA. 
179 
form a new one from the scanty materials thus obtained, and 
the danger of mistaking variable characters for specific differ- 
ences, so apt to occur even where every facility is afforded, is 
so great, that attempts of this kind should be discouraged. 
We shall first investigate the history of the species which 
form the Alexandrian Senna of commerce. In the compo- 
sition of this prepared article, it is admitted that two distinct 
species of Cassia are to be detected. One of them with acute, 
the other with obtuse leaves. Although the difference be- 
tween these two was known to Linn^us, yet he chose to 
look upon the distinction as variable, and therefore compre- 
hended both under the name of Cassia Senna, considering 
them as varieties of one species. At that period the acute 
leaved Senna Was known by the specific name of Alexandri- 
na, and the obtuse leaved one by that of Italica. In the same 
way they had been regarded by the older authorities, and 
Morison in his Hist. &c. has given figures of both varieties; 
his work was published in 1680. 
Lamarck in the Dictionaire Methodique, Art. Cassia, sepa- 
rated these two varieties into distinct species, and upon 
the authority of Forskall called the plant with acute leaves, 
Cassia lanceolata, while he still retained for the one with 
obtuse leaves the term Cassia senna. In this state our 
knowledge of the plants yielding the Alexandrian Senna re- 
mained until the period of the memorable invasion of Egypt 
by Buonaparte. A commission was then formed to investi- 
gate the Natural History, as well as the monuments of Art of 
this most interesting country. The commission formed itself 
into an Institute well known by the scientific world as the 
Institute of Cairo. To the labours of this body much credit 
is due, and not the least portion of it to the individuals who 
devoted themselves to the Botanical department. 
The investigation of the genus Cassia appears to have occu- 
pied a prominent place in their estimation, as two members 
of the commission have deemed it of sufficient importance to 
devote separate essays to it; each of them presenting the facts 
which came within the sphere of his personal observation. 
