PREFACE. 
Tuis work, which has been ten years in execution, would have 
been long since brought to a close had the subject been less diffi- 
cult, or one which demanded less exact examination. It has, how- 
ever, proved a most laborious task to examine with the necessary 
care so large a number of plants of a very intricate structure, in a 
dried state; and the author's other engagements have left him 
little leisure for the steady prosecution of this enquiry, so that it 
has been impracticable to advance with greater speed. 
This explanation is due to those friends of science whose collec- 
tions have been entrusted to the author for all this long period. 
He regrets, however, to add that, during the ten years that have 
elapsed since the appearance of the first part of the work, his 
materials for the classification of Malaxez, Epidendrez, and Van- 
deze, have so much increased by the acquisition of species in his 
herbarium, or by the introduction of living plants to the gardens 
of Europe, as to render a reconsideration of those tribes indispen- 
sable. This will take place in a Revision of the Order, which is 
even now in preparation, and which, if his life is spared, may be 
expected to appear about two years from this time, illustrated with 
numerous figures of genera. In that work will be incorporated all 
the author's recent acquisitions, with such others as, in the mean- 
while, may be sent him; and an attempt will be made to sub- 
divide the other tribes, upon the same principles as have been 
adopted in the classification of Neottez. ‘The author will be very 
grateful for assistance; but he finds it necessary, in consequence 
of the great numbers of dried plants sent him for determination, 
to be returned to the owners, to condition that, from this time for- 
ward, with the exception of those in his hands at the present time, 
he shall not be expected to return the dried plants, which his 
correspondents may send for names, but that he shall have full 
