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IX. — A New Aj^rangement of the Genera of 
Mosses, with Characters, and Observations on 
their Distribution, History, and Structure. 
By R. K. Greville, Esq. F.R.S.E. M.W.S. , 
AND 
G. A. Walker Arnott, Esq. A.M. F.R.S.E. 
{Read 2Sd February 1822.) 
Memoir I. 
Before we proceed to the definition of the Order, we 
shall offer some preliminary observations on the principal 
parts, of which we avail ourselves in the construction of 
generic characters, and the formation of natural groups. 
It is well known, that the great distinguishing character 
between acotyledonous or exembryonate plants, and all 
other vegetable tribes, is, as the name imports, the absence 
of any cotyledon in the embryo, or, more properly, the en- 
tire absence of the embryo itself. In all cotyledonous 
plants, stamens and pistils are invariably present : on the 
contrary, in the acotyledonous orders, they are to all ap- 
