202 MB. G. BENTHAM ON OECHIDE^E. 



species of Pleurothallis itself, where the creeping caudex is 

 stem-like and the peduncles and unifoliate stems or branches 

 appear distinct, but are, in fact, joined together from the same 

 node. 



The Pleurothalleae are all tropical American, and include, 

 according to present estimates, above 600 species in ten genera' 

 very fairly characterized, and, as to the great majority of species' 

 readily distinguished from each other. Pleurothallis itself com- 

 prises about 350 species ; and from amongst them it has been pro- 

 posed by various authors to separate eight genera, mostly mono- 

 typic or nearly so, which, however, Lindley, in his latest monograph 

 in the ' Folia Orchidaceae,' has again reunited. He there distributes 

 the species into ten series, which, for the ' Genera Plantarum,' I 

 have somewhat modified and reduced to seven. Stelis (including 

 Dialissa, Lindl.) with about 150 species, Lepanthes with 40, and 

 the smaller genera Phjsosiphon and Octomeria remain intact. 

 There has been some difficulty in the distinction between Bestrepia 

 and Pleurothallis, however marked it may be in some cases. 

 Lindley was disposed to rely chiefly on the curious antenna-like 

 form of the petals in some species ; but this character is much too 

 vague in others. Eeichenbach would fix absolutely on the number 

 of pollen-masses— two (one in each cell) in Pleurothallis, four in 

 Bestrepia ; and, as far as is at present known, this may be the 

 safest course to pursue ; but the separation is not always natural, 

 and perhaps not always quite definite. In P. tubulosa, for instance^ 

 which is clearly a Pleurothallis, Lindley found four pollen-masses 

 although in two specimens I examined I could only find two ; and 

 there are a large number of minute-flowered species in which the 

 pollen has not been accurately observed. True Bestrepias appear 

 to have always single one-flowered peduncles ; whilst true Pleuro- 

 thallises have usually (but by no means always) a racemose or 

 clustered inflorescence. 



Distinct as the characters are, both vegetative and floral, which 

 separate Masdevallia from Pleurothallis, there is one species which 

 has apparently with equal right been published by Lindley himself 

 in both genera— Pleurothallis purpurea or Masdevalliafenestrata. 

 It has the stem elongated below the leaf and the sepals without 

 spreading points, as in Pleurothallis ; but the flowers are large, 

 as in Masdevallia, under which genus it has been figured and has 

 established itself in our collections. Brachionidium, Lindl., is a 

 small genus evidently allied to Masdevallia, but requiring some 



