5o8 



NATURE 



{Sept. 5, 1878 



appearance, and perhaps even of varying morphological sig- 

 nificance. 



On the Inflorescence of Senebiera didyma, by Prof. Alexander 

 Dickson, M.D. — When at Plymouth last August during the 

 meeting of the British Association, I took the opportunity of 

 examining Senebiera didyjna, a weed which grows in great 

 abundance on road-sides and waste places about the town, and 

 I was much struck with a remarkable peculiarity to be observed 

 in connection with its inflorescence. 



The inflorescence is like that of the mass of cruciferous plants, 

 racemose. The racemes are " opj^ositifoliar," and at first sight 

 the arrangement seems to be analogous to that of the oppositi- 

 foliar inflorescences of Vitis or of Alchemilla arvensis, where the 

 inflorescence is really terminal, but thrown to the side by pre- 

 ponderant development of a "usurping shoot," the axillary bud 

 of the last leaf produced by the primary axis before ending in 

 the inflorescence. This view seems further supported by the 

 fact that of all the foliage leaves, that opposite the raceme is 

 the only one apparently destitute of an axillary bud, which on 

 the supposition would be represented by the '' usurping shoot." 

 If, however, the plant is more closely examined, a very remark- 

 able condition is disclosed, one, indeed, which off"ers a morpho- 

 logical problem of considerable difficulty, and which, probably, 

 can be effectually solved only by developmental study. The 

 peculiarity consists in the constant occurrence of a solitary flower 

 springing somewhere from the internode below the raceme 

 either about half way down towards, or almost close to the level 

 of the leaf below. So far as my observations go, the solitary 

 flower is never quite as low as the level of the lower leaf. It 

 might be supposed that from almost immediately above the second 

 last leaf of the main axis, the bases of the terminal raceme of 

 the "usurping shoot, "and of the axillant leaf of that shoot had 

 all become fused together. Now, although cases are known on 

 the one hand, of adhesion between the base of a terminal flower 

 and that of the usurping axis [e.g., Helianihemum vulgar e. 

 Payer), and, on the other hand, between the base of an axillant 

 leaf and that of the usurping shoot in its axil [e.g. Sedum, sp. 

 Payer), we do not know of connation of all three together. It 

 is possible, but I think improbable. 



The view which, after careful consideration, occurs to me as 

 most fully satisfying the conditions of this remarkable case, may 

 be stated briefly in categorical form as follows : — 



1. The racemose inflorescence is terminal and properly begins 

 just above the level of the "second last " leaf. It would thus 

 include the aforesaid solitary flower. 



2. The raceme, after producing one ebracteate flower, pro- 

 duces at its second node a foliage leaf from whose axil the 

 " usurping shoot " springs. 



By such an explanation we can dispense with any cumbrous 

 adhesion hypothesis such as I have indicated above. The pecu- 

 liarity is that the main axis does not, per saltum, pass from the 

 condition of a leafy axis to that of an axis of inflorescence, but 

 begins by producing one flower and then developing a foliage 

 leaf beyond which the series of flowers is uninterrupted. The 

 "usurping shoot," as above indicated, represents the axillary 

 bud of the foliage leaf by which the raceme is interrupted. 



On the 6-cclled Glands of Cephaloius and their Similarity to the 

 Glands of Sarracenia purpurea, byProf . Dickson. — Dr. Dickson 

 pointed out that the peculiar 6-celled glands found on the ex- 

 ternal surface of the pitcher, both surfaces of the pitcher -lid, 

 and both surfaces of the foliage -leaf of Cephalotus are very 

 nearly identical in structure with the glands on both inner and 

 outer surfaces of the pitcher of Sarracenia purpurea, which were 

 originally described by August Vogl. Dr. Dickson suggested 

 that the remarkable resemblance in this respect, taken in con- 

 nection with certain correspondence in the details of the insect- 

 trapping apparatus miglit suggest an affinity not hitherto 

 suspected. 



Exhibition of Plants of Isoetes echinospora. — Dr. Dickson 

 exhibited specimens referable to this species which he lately 

 found growing on muddy bottom among Potamogeton in about 

 two feet of water in Loch Callater, Aberdeenshire. The plants 

 were remarkable for the very slender and tapering character of 

 the leaves which curve outwardly. The spores are very mark- 

 edly echinate, and in diameter about one-fourth smaller than 

 those of /. lacustris. 



Dr. Moore, Glasnevin, exhibited remarkable specimens of 

 an Isoetes from Lough Bray, co. Wicklow. They were of 

 great size, much above the average of specimens of /. lacus- 

 tris. Prof. Suringar and Prof. M'Nab suggested that it 



might be the same as the Italian species known as Isoetes inalin- ' 

 verniana. 



Mr. Britten exhibited, on behalf of Mr. J. H. A. Jenner, 

 specimens of Ruvux viaxiimis, Schreb, from a new locality on 

 the Cuckmere River, East Sussex. The specimen sent showed 

 the various characters by which R. niaximus can be distinguished 

 from R. hydrolapathum, the species with which it has been 

 confounded. 



Dr. Bayley Balfour exhibited, on behalf of Mr. Sadler, speci- 

 mens of Salix Sadleri and Carex frigida obtained at the beginning 

 of August in Corrie Chandler, Aberdeenshire. These plants 

 were discovered in 1874 by Mr. Sadler, and have not been met 

 with again until this year. 



Notes on Naiadacea, by Dr. Bayley Balfour. — Dr. Balfour 

 more particularly described some of the peculiarities observed 

 by him in the genus Halophila, an extremely interesting tropical 

 phanerogamous plant. 



Dr. Price, of Chester, sent for exhibition portions of the 

 leaves of Cardamine pratensis producing numerous gemmae. 



On the Supposed Radiolarians and Diatoviacecc of the Coal- 

 Measures, by Prof. W. C. Williamson, F.R.S.— Prof. W. C. 

 Williamson called attention to the Traquarice of Mr. Carruthers, 

 found in the lower coal-measures of Lancashire and Yorkshire, 

 Avith small spherical objects that observer believes to be radio- 

 larians like those still living in existing seas. Prof. Williamson 

 showed that the radiating projections with which these spheres 

 are surrounded were not siliceous spines like those of the 

 Radiolarise, but extensions of a continuous membrane which 

 enclosed the entire organism, and which therefore could not have 

 the spicular nature attributed to them. He then demonstrated 

 that within this external membrane is a second inner one, which 

 latter is filled with numerous small vegetable cells, like others 

 shown to exist in the interior of fossil spores and reproductive 

 cryptogamous capsules, found in the same beds as those which 

 fxirnish the Traquarice. 



These conditions are so different from those existing in any 

 known recent species of radiolarian as to lead Prof. Williamson 

 to reject the idea of their radiolarian character ; -whilst their 

 close organic resemblance to some obviously vegetable concep- 

 tacles found in the same coal-measures suggest that the Traquarice 

 are also vegetable structures. 



The mountain limestone deposits of some British localities 

 contain a vast multitude of minute calcareous organisms which 

 Mr. Sollas and other observers have regarded as radiolarians. 

 These structures, however, seem to exhibit no satisfactory evi- 

 dence of being so. In the first place these organisms are now 

 calcareous instead of siliceous. It has been suggested that their 

 siliceous elements were removed, and replaced by carbonate of 

 lime, but this appears to be most improbable. 



Prof. Roscoe and Prof. Schorlemmer agree in stating that 

 they would require overwhelming evidence before they would be 

 prepared to accept such an explanation of the present condition 

 of these objects or of the fact of the substitution of carbonate of 

 lime for silica, that such an explanation renders necessary. 



Count Castracane has published an account of a process by 

 which he reduced numerous specimens of coals to very minute 

 quantities of coal-ash, and has stated that he found in these ashes 

 numerous marine and fresh-water diatomaceae. Prof. Roscoe 

 kindly allowed one of his ablest assistants m his laboratory at 

 Owens College to prepare analyses of a number of coals accord- 

 ing to Count Castracane's method. The residual ashes of these 

 preparations have been mounted microscopically by Prof. 

 Williamson, and in no one of them can a trace of a diatom be 

 found. Beyond stating the fact he is wholly unable to account 

 for the discrepancy between his results and those of the Italian 

 observer, so far as his present observations go, he finds himself 

 compelled to conclude that we^have no proof of the existence of 

 radiolarians or of diatomacere in the British carboniferous 

 rocks. 



A short discussion ensued, in which Sir Joseph Hooker, Prof. 

 M'Nab, and Dr. Bayley Balfour took part, the views expressed 

 coinciding generally with those of Prof. Williamson. 



On the Association of an Inconspicuous Corolla with Frotero' 

 gynous Dichogamy in Insectfertilised Flowers, by Alex. S. 

 Wilson, M.A., B.Sc. — The majority of conspicuously- coloured 

 flowers whose cross -fertilisation depends on their being easily 

 seen by insects, are proterandrous. Such plants have their 

 flowers placed in close inflorescences, as, for example, in Erica, 

 Calluna, Vaccinium, Digitalis, Linaria, Gladiolus, &c., and 

 occasionally the flowers are secund, or placed on one side of 



