TRANSACTIONS OF THE SECTIONS. 157 



General Hemarls on the Geological Structure and Flora of the Mascarene 

 Islands. By I. Batlet Balfour, D.Sc. 



The geological structure of the principal islands of the Mascarene group, viz. 

 Bourbon, Mauritius, and Rodriguez, was briefly described. These islands are all 

 of volcanic origin, the rock being chiefly a very dark compact basalt. Each island, 

 however, has not been altogether formed at one period. This fact is particularly 

 well illustrated in Bourbon, where the N.AV. portion is of more ancient date than 

 the S.E., in which latter part there exists at present an active volcano. Consequent 

 on this difference of age the rocks are of a diflerent character ; and this has a corre- 

 sponding effect upon the vegetation of the two districts. These differences are 

 such as characterize the flora of a dry as opposed to a moist region. 



The type of the Mascarene flora was shown to be Indian, although the islands 

 are nearer to the African continent than to India ; and the comparative absence of 

 endemic types was indicated. 



After detailing several facts regarding resemblances betwixt the floras of the 

 islands, and a brief reference to their fauna existing and extinct, the author indi- 

 cated the bearings of the geological structure and of the flora upon the question of 

 the separate origin of the islands, or of their being merely fragments of a preexisting 

 continent which also embraced Madagascar and the Seychelles. 



On an Abnormality of Primxila vulgaris with Interpetaline Lobes. 

 By Prof. A. Dickson, M.D. 



The abnormal flowers exhibited were collected in 1874 at Pitlochrie, Perthshire, 

 by the late Professor Inglis, of Aberdeen. The peculiarity consists in the develop- 

 ment of five narrow petaloid segments, which alternate with the lobes of the corolla. 

 These are not organs simply adherent to the inner surface of the corolla-tube like 

 " epipetalous " stamens, but their bases form a continuous sheet of tissue with the 

 petals. At first sight the abnormality appears to resemble the " doubling " of the 

 primrose often seen in cultivation. In the ordinary double primrose, however, the 

 additional petaloid lobes are metamorphosed stamens, and are opposite to (not 

 alternate with) the lobes of the corolla. In the abnormality exhibited the super- 

 added petaloid pieces are simply interpetaline lobes analogous to the intersepaline 

 lobes of Nemophila, Campanula medium, &c. One of the most interesting points 

 connected with this is that in the order Primulaceee we have a genus, Soldanella, in 

 which interpetaline lobes occvir. In S. montana, for example, the limb of the 

 corolla exhibits five broader lobes, which are trifid, and five nan-ower ones, which 

 are entire. The five trifid lobes represent the petals proper, while the five entire 

 ones are interpetaline lobes. In the monstrous Primula we have thus an abnor- 

 mality imitating, so to speak, the normal condition of an allied genus. 



On a Monstrosity in Saxifraga stellaris. By Prof. A. Dickson, M.D. 



The plant from which the specimens exhibited were obtained was found bv 

 Dr. A. P. Aitken, of Edinburgh, in July last, on Ben Challum near Tyndrum. It 

 had three flowering stems, which about their middle exhibited a few scattered 

 nan-ow bracts with what appear to be viviparous buds in their axils. Each of 

 these stems is terminated by a monstrous flower, with somewhat numerous sepals 

 in several series. Petals absent ; stamens about as many as the sepals ; and a vast 

 number of separate carpels, forming- an apocarpous gynfficium almost like that in 

 Ranuncidus. This monstrosity is almost exactly parallel to the monstrous flowers 

 not unfrequently found terminating the inflorescence of Digitalis purpurea, where 

 we have a multiplication of the parts of the floral envelopes and andrcecium, and a 

 pistil composed often of several whorls of cai-pels. 



On Abnormal Flowers of Tropseolum. By Prof. A. Dickson, M.D. 



