PHANEROGAMS — PROFESSOR BAYLEY BALFOUR. 161 



Thus the Aden plant has been confounded with the Ad. obesum, Roam, and 

 Schult., and with Ad. Honghel, DC, from both of which it is different, and 

 these latter species have also been confounded together. The Aden plant has 

 been more recently figured in the Botanical Magazine, t. 5418, as Forskal's plant, 

 under the name Ad. obesum. Here, again, there is confusion ; the figure is 

 rightly enough the Aden plant, but the description is inapplicable, and is that 

 of the true Ad. obesum, Roem. and Schult. 



The fact is, there are two Arabian species, the old Ad. obesum, Roem. and 

 Schult., not known from Aden, and the Aden plant, to which we must now give 

 a name, and I propose Ad. arabicum. They are both quite distinct from Ad. 

 Honghel, DC 



Fenzl (Diagn. iEthiop. in Kais. Akad. "Wiss. Wien, li. (1865), 140) diagnoses a 

 form from ./Ethiopia, as Ad. speciosum, distinguishing it from Ad. Honghel, DC, 

 by its general pubescent character, and the subracemose flowers. From the 

 glabrous Ad. Honghel, DC, the form is quite distinct, but I cannot separate it 

 from Ad. obesum, Roem. and Schult., which is quite as tomentose, and the sub- 

 racemose floral arrangement is worth little, for one finds there is a tendency in 

 all species to elongation of the rhachis ; indeed Roemer and Schultz's original 

 description speaks of the inflorescence as a corymb. Fenzl's plant, then, I take 

 to be merely Ad. obesum, which is thus not an endemic Arabian form. 



The east tropical African plant, Ad. multiflorum, Klotzsch, is a form quite 

 distinct from the above three species, and readily distinguishable by its glabrous 

 leaves with veins conspicuous below, and the corolla tube internally lined with 

 hairs. With it our Socotran plant appears conspecific. 



In Kew Herbarium some specimens from Somali Land belong to a very 

 distinct form, which may be described as new under the name Ad. somalense. 

 It is readily distinguished by its almost linear glaucous leaves. There is but 

 one flower on the plant, and I have hesitated to dissect it ; but it apparently 

 wants the hairy lines at the base of the corolla tube inside. 



Resides these I have mentioned, the genus is represented in south Africa by 

 some forms distinct specifically, but of which material is not yet forthcoming 

 for complete diagnosis. 



It may be well if I now give concisely the synonymy of the several species 

 I have mentioned above, with a short diagnosis of each. 



A. obesum, Roem. et Schult. Syst. iv. xxxv, and 411 ; G. Don'" Syst. iv. 

 80 ; Alph. DC Prod. viii. 412 ; Hook. Bot. Mag. descr. sub tab. 5418, non. ic. 



A. speciosum, Fenzl Diagn. iEtluop. in Kais. Akad. Wiss. Wien, li. (1865), 140. 

 Nerium obesum, Forsk. Fl. iEgypt. Arab. 205 ; Vakl Symb. ii. 45. 



* Alph. De Candolle quotes Don, and in tins lie is followed by T. Anderson, and in the Botanical 

 Magazine, as referring this plant to the genus Pachypodium. But I cannot discover this. Don rightly 

 enough writes of Adenium (or Adenum) obesum, but in a note he says, " See Pachypodium, p. 78, 

 for culture and propagation," and this may have originated the mistaken quotation, 



TRANS. ROY. SOC. EDIN. VOL. XXXL X 



