ii8 



SCIENCE-GOSSIP. 



which delights in the most arid situations. The 

 same holds good in the case of the species of 

 Nasturtium. In iV. sylvestre, growing on the river 

 bank, the leaves are often cut into narrow segments, 

 but in A'', officinale the leaf divisions are broader. 

 Two forms of the latter plant occur, siifolium, which 

 grows in damper places than microphyllum, having 

 the leaf-segments much broader than those of its 

 relative from drier situations. 



The sg,me difference is markedly displayed in the 

 case of Lathyrus 7nacrorrhizus , and its variety 

 tenuifolius. Many of the damp-loving saxifrages 

 develop broad slightly divided leaves, but Saxifraga 

 tridactylites, with its narrowly-cut leaves luxuriates 

 on dry banks and walls. Other instances too 

 numerous to mention will occur to most botanists ; 

 at the same time, no doubt, exceptions occur in 

 which the converse, as noticed by Mr. Griset, holds 

 good. Perhaps the best method of demonstrating 

 the effect of dryness and humidity would be to 

 trace the vagaries of individuals of a single 

 polymorphic species, such as Taraxacum officinale or 

 Capsella bursa -pastoris, in various habitats ; and if 

 this was done, I venture to predict that ceteris 

 paribus, those occupying the driest situations, would 

 exhibit the least development of parenchyma. It 

 is probable that other influences, such as the 

 amount of light and shade, cold and heat, available 

 plant food in the soil, and heredity, would have to 

 be taken into account in any serious attempt to 



determine the true reason of the remarkably diffe- 

 rent shapes assumed by the leaves of individuals of 

 certain species of plants. 



The large, slightly pinnatifid leaf of Taraxacum, 

 illustrated by fig. i, is from a damp ditch, and was 

 growing almost in the water ; fig. 2 represents 

 leaves gathered from the dry summit of the 

 embankment of the same ditch ; and the third 

 sketch is the leaf of a dandelion found at the foot 

 of an adjacent wall, which was sheltered from the 

 rain on two sides. Fig. 4 represents one of the 

 delicately divided leaves of Taraxacum erythro- 

 spermum from the dry, barren sand-dunes of the 

 Lancashire coast. An example afforded by a 

 different genus is a leaf of Serratula tinctoria 

 (fig. 5), which was collected on the river bank at 

 Aysgarth (North Yorks). Contrasted with it is the 

 leaf of an interesting small form of the same 

 species (fig. 6), of which I have excellent specimens, 

 collected on the Freshwater Downs by the late 

 Captain Steuart. Although in this one matter I 

 cannot quite agree with Mr. Griset's observations, 

 I must express my thanks to him for the pleasure 

 I felt in the perusal of his very interesting bit of 

 botanical " gossip." It opens up an enticing line 

 of study, one that can be followed amongst 

 the common weeds accessible to the botanist 

 whose lot, like mine, is cast in the suburbs of a 

 large city. 



H. M. Prison, Liverpool. 



UNIO LITTORALIS IN PLEISTOCENE TIMES. 

 By a. S. Kennard. 



T N considering the question of the former 

 occurrence of any species, too much stress 

 cannot be laid on the imperfection of the geological 

 record. Fossiliferous Pleistocene deposits are 

 extremely rare in this country. We have no such 

 well-developed beds as we have of the Cretaceous 

 or the Eocene. On the contrary, they are always 

 fragmentary, small patches, which by chance have 

 escaped the enormous denudation which we know 

 has occurred in, geologically speaking, recent 

 times. Even when this danger has been escaped, 

 the enclosed fossils are very often in such a 

 fragmentary condition that the true specific 

 determination is a matter of doubt. Though of 

 small extent and rarely of any thickness, yet there 

 is every reason to believe that these beds indicate 

 a vast elapse of time. The complete series are 

 probably represented in the Crayford beds, which 

 are no more than a hundred feet thick. To the 

 Malacologist they are of great importance, as in 

 them are found for the first time many species of 

 British Mollusca, while several which were then 



abundant are now quite extinct with us, though 

 occurring on the Continent. 



Unio littoraUs, Lamk., was first described as a 

 British fossil by Mr. G. B. Sowerby, in 1838, from 

 specimens in the collection of Professor J. Morris. 

 There is apparently an error as to the exact locality 

 from which these examples were obtained. In the 

 list, the species is only noted as being found at 

 Erith, but Grays is given against the figure. 

 It certainly occurs in both places ; but while it is 

 abundant at Erith, it is extremely rare at Grays, 

 so that in all probability the former is the correct 

 locality. Since its first discovery it has been 

 recorded from Crayford, Barnwell Abbey and 

 Grantchester, near Cambridge, Clacton, Crop- 

 thorne, near Evesham, Westminster, Ilford, 

 Brentford and near Walton -on -the -Naze. At 

 Grays, as mentioned above, it is very rare. In 

 1882, Mrs. S.V.Wood, jun.. noted that although Unio 

 tumidus, Retz, swarmed at this locality, he could 

 never find U. littoraUs, Lamk. ; though Sir Charles 

 Lyell sent his father some specimens of it, which 



