tachyon is the type of Dr. Hooker's genus Polystachya ; 
D. wtricularioides, and probably testiculatum, are species of 
lonopsis; D. palmifolium and Barringtonie belong to the 
genus now reformed. Of the few remaining after these 
deductions, the East Indian kinds are probably genuine 
species of Dendrobium, and most of the others require 
further examination. 
The genus Dendrobium, as limited by Mr. Brown in the 
2d edition of the Hortus Kewensis, should include no species 
except those with 4, parallel, distinct pollen-masses ; and 
will consequently contain only the East Indian species, 
which form a numerous group, distinctly characterised by 
the character above mentioned, and naturally connected 
by habit. _ They are trailing or erect parasites, without 
bulbs, but with long, leafy, or naked round stems, producing 
the flowers from their axilla, either singly, or in few- 
flowered fascicles. From these, the American species, 
agreeing with them in general structure of perianthium, 
are now divided. They are distinguished by having only 
two pollen-masses, each divided down the mdidle, and 
connected at the base by a common glandular process; and 
by being all bulbous. Besides the kind now published, 
_D. Barringtonie (Mazillaria Barringtome Nob.) and 
D. palmifolium (JZ. palmifolia Nob.), belong to the genus 
Maxillaria, which will be increased by the examination of 
the numerous Dendrobium-like plants of the continent of 
South America. It is distinguished from Polystachya by 
the structure of its perianthium, and by its radical in- 
florescence. 
Nearly related to Maxillaria, in general characters, and 
in geographical position, is a genus of which the plant 
published at tab. 732 of this work, under the name of 
Dendrobium squalens, must be considered the type. This 
plant has only two pollen masses, furrowed on each side, 
and its flowers are in their natural position. It may be 
called Xylobium, and thus characterised : 
XYLOBIUM. 
Perianthium rectum, patens. Labellum cum processu unguiformi co- 
lumne articulatum, trilobum, in columna incumbens.  Sepala lateralia 
exteriora basibus cum processu columne connata. Pollina 2, hinc sulcata. 
——Herbee habitu Masxillarie. 
Sp. 1. Xylobium squalens. 
Dendrobium squalens. Supra t. 732, 
Vj 1G, 
