52 Prof. Lindley upon the Genus Decaisnia. 



cause of the movement to excitable globules contained in the 

 fluid of what he calls the cylindrenchyme of the stigma ; this 

 fluid being carried to the extremities of the cylindrenchyme, 

 these extremities are dilated, which causes the stigma to bend 

 in one direction ; but when the stigma is touched, the globules 

 and the liquid flow back to the bottom of the cylinders, and 

 in this case, this side becoming the longest, the style erects 

 or bends in an opposite direction : M. Morren therefore re- 

 fers the cause to the excitability of a vital fluid. 



In examining the stigmata of Diplacus puniceus and the 

 different species of Mimulus, in order to ascertain if they con- 

 tained any analogous structure to that described by M. Mor- 

 ren, I found the inner surfaces of the stigmata in all com- 

 posed of elongated cylindrical cells, the ends of which are free 

 and prolonged into tapering jointed glandular hairs : these 

 hairs, which thickly clothe the surface of the stigma*, are di- 

 lated at the extremities, and at the base where they arise each 

 one forms a thickened elbow, with the cell of which it is the 

 termination. 



When the plates of the stigma are in their natural position 

 these hairs are erect, but on examining them after the plates 

 had collapsed, I found them gathered together into bundles 

 of a dozen or more with their points drawn closely together, 

 and in some cases twisted spirally round one another : in the 

 stigma of Mimulus roseus each hair was recurved over its own 

 cell. It is easy to conceive that such a movement of the hairs, 

 forming as they do the extremities of the cylindrical cells, 

 would cause the stigma to incline inwards, and it is probable 

 that the natural cause of their movement is, as M. Morren 

 asserts, the reaction of an excitable fluid. 



I am, Sir, your obedient Servant, 



Joseph Henderson. 



Milton, near Peterborough, July 13, 1840. 



VII. — A Note upon the Genus Decaisnia, Ad. Brong. By 

 Professor Lindley. 



This genus, founded upon a Brazilian plant from the Island 

 of St. Catharine's, was published by M. Adolphe Brongniart 

 in the Botanical part of Duperrey's Voyage. It was admitted 

 into the Neottideous tribe of Orchidaceae in my Natural Sy- 

 stem of Botany, and by Endlicher has been equally adopted 

 as a genus of the Arethuseous tribe. 



* In the stigma of Goldfussia anisophylla these hairs are shorter, more 

 thickly crowded together, and less dilated at the points than in stigmata of 

 Mimulus and Diplacus. 



