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IX. On the Modifications of Æstivation observable in sith Plants, formerly 
referred to the Genus Cinchona. By Mr. Davin Don, Libr. L.S. 
Read April 2nd, 1833. 
THE various forms of zstivation appear to depend, in a great measure, on 
the relative position and development of the organs of reproduction; for we 
have remarked that the valvate kind occurs most frequently in such flowers 
as have those organs much enlarged and projecting beyond the mouth of the 
tube of the corolla, or where there exists any considerable inequality in length 
between the stamina and pistillum. It is much more varied in monopetalous 
than in polypetalous flowers ; for, with the exception of a portion of the Ruta- 
cec, principally from New Holland and South America, the imbricate form is 
found generally to prevail in the latter class. In the valvate form the pieces, 
having their edges sloped in opposite directions, are nicely fitted together, 
affording not only the most complete protection to the delicate organs within, 
but also ample space for the development and subsequent impregnation of the 
stigma. 
Among the monopetalous orders the form of estivation is a character of 
such high value as oftentimes to afford the only palpable distinction to the 
limitation of families; but the extensive order Rubiacee presents a striking 
exception, examples of almost every modification of zstivation being afforded 
by it. The Rubiacec appear to constitute a grand central point of union (of 
which several may be remarked in the vegetable kingdom,) between the fami- 
lies of the monopetalous class; and possessing great diversity of form and 
character, they are found to partake more or less of the habit and structure of 
those orders to which they are related. The Rubiacee are intimately allied 
on the one hand to Caprifoliacee and F'alerianee, and on the other to Apo- 
cynece and Gentianew, being distinguished from the two former by their sym“ 
metrical flowers, and from the latter by their adherent ovarium and undivided 
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