Mr D. Don on the Melastomacew. 69 



nera whose anthers terminate in a tubular process, as Melas- 

 toma, Osbeckia, Rhexia, Arthrostemma^ &c. in which the 

 cells of the anthers are attached along the inner surface of an 

 elongated connectivum, and are plaited and wrinkled, so that when 

 the anthers issue from their receptacle (being forced out by the 

 development of the pollen swelling the cells), the pollen is 

 thrown out with an elastic force, the transverse rugae materially 

 assisting in its discharge. In Melastoma, the alternate anthers, 

 which are also the largest, and placed opposite the septa, are 

 attached by means of the elongated base of the connectivum to 

 the filaments, as it were to a pivot, which gives additional force 

 to the emission of the pollen. In BlaJcea, Cremanium, and other 

 genera, which have their anthers truncate, and opening by two 

 terminal pores, the hollow spaces are entirely wanting, the tube 

 of the calyx and ovarium being completely united, and the sta- 

 mina in the unexpanded flower being arranged in the free space 

 between the summit of the ovarium and limb of the calyx. 

 The union of these two organs is still more complete in Cha- 

 rianthus, in which, as the dehiscence of the anthers is longitu- 

 dinal, and no force is required for the emission of the pollen, 

 the anthers are found to be merely bent downwards in aestiva- 

 tion, to prevent their being pressed upon by the sides of the pe- 

 tals. 



I take this opportunity of correcting an error {first pointed 

 out to me some years ago by Mr Brown) into which Ruiz, Pa- 

 von, and myself have fallen, in considering the two protube- 

 rances at the base of the leaves of Aa:lnaa glandulosa as glands, 

 while in fact they are merely callosities, originating in the fold- 

 ing backwards of a portion of the leaf. 



EXPERIMENTS UPON THE SOLIDIFICATION OF RAW GYPSUM. 



By John P. Emmet, Professor of Chemistry in the Uni- 

 versity of Virginia. 



The facility with which burnt gypsum sets, when made into 

 a paste with water, has rendered it not only conspicuous among 

 minerals, but highly useful in the arts ; hitherto, however, as 



