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XIV. On the Origin and Nature of the Ligulate Rays in Zinnia ; 

 and on a remarkable Multiplication observed in the Parts of 

 Fructification of that Genus. By Mr. David Don, Libr. L.S. 



Read November 18, 1828. 



The ligulate rays of Zinnia consist of a foliaceous, persistent, 

 coloured, and highly vascular membrane, with rough, spinously- 

 denticulated edges. They are traversed by two principal trunks 

 of vessels almost parallel to their margin, which branch out 

 into innumerable ramifications through the disk. These trunks, 

 which are composed of proper and spiral vessels, may be very 

 distinctly traced from the limb of the ray downwards along the 

 two prominent edges of the ovarium. The vessels become more 

 apparent on the withering of the rays, and the beautiful arrange- 

 ment of their ramifications constitute then an interesting object. 

 The principal trunks of vessels, thus occupying both sides of the 

 lamina, tend to extend them so considerably beyond the centre, 

 as to constitute frequently two distinct lobes. The want of arti- 

 culation in the tube, visible in the florets of the disk, their con- 

 sistence, and the disposition of the vessels, and their ramifica- 

 tion, — a disposition which is found precisely the same in the 

 central ovaria, — would seem to prove that the rays of Zinnia 

 are an elongation of the exterior cortical layers of the ovarium, 

 which in the centre florets are developed into a species of pa- 

 leaceous pappus, which is not present" in the ray florets. The 

 peripherical ovaria are frequently triquetrous, and each of the 



edges 



