2 ONCIDIUM. 



South America a very small proportion of them have remained 

 denizens among us for any length of time. 



The following diagnosis from the Genera Flantarum defines the 

 extent of the genus : — 



The sejmls are generally sub-equal, spreading or reflexed ; they are 

 either all free or the lateral two are connate at their base ; in some 

 species the lateral sepals are much longer and narrower than the 

 dorsal one. 



The petals are either similar to the dorsal sepal or larger. 

 The Up is affixed to the base of the column by a short claw that 

 is divergent or spreading ;* the side lobes are adnate to the claw and 

 usually small or obsolete, the intermediate lobe is spreading, very 

 broad, emarginate or bifid (in the section Microchila entire, narrow 

 and reflexed) ; the disk at the apex of the claw is conspicuously crested 

 or tuberculate. 



The column is short and thick, with a petaloid wing on each side 

 of the stigma, below which there is a prominent protuberance. 



The pollinia are two, globose or inversely egg-shaped, united to the 

 gland by linear or flattened caudicles (stipes). 



The capsule is usually ovoid-oblong, sometimes fusiform, more or less 

 rostrate. 

 Generally. — The essential characters of Oncidium are the short 

 thick winged column that is nearly always tumid below the stigma, 

 and the tuberculated or much-toothed crest of the labellumjt the 

 first -named character chiefly separates it from Odontoglossum and 

 the latter from Miltonia. Besides these there are characters in the 

 habit and inflorescence by which cultivators recognise many species 

 of Oncidium. 



The vegetative organs of Oncidium are essentially the same as 

 those of Odontoglossum, and are fully described under that genus; 

 it is here only necessary to notice some of the most obvious 

 deviations that occur in the cultivated species. 



In Oncidium zehrinum, and in a less degree in 0?i. Jfexuosum, the 

 rhizome is much developed and becomes scandent. In 0?i. Papilio, 

 On. Kramerianum, On. ampliahnn, and one or two others, the pseudo- 

 bulbs are disk-like with the sides more or less corrugated. On. hicallosum, 

 On. carthaginense, On. Cavendishianum, On. Lanceanum, On. luridum 

 and two or three other allied species are without pseudo-bulbs, but 



* In Odontoglossum the claw of the lip is always parallel with the face of the column. 



+ This is an important character in the determination of species, but often so complicate 

 in structixre as to render it extremely difficiilt to describe. In cases of doubt the reader should 

 always refer to a good drawing of the species when one is accessible. 



