346 report— 1879. 



much facility for equalisation of temperature by currents between the colder water 

 above and the warmer water below, that they furnish no useful results. Even in 

 bores of small diameter the same disturbing cause exists, and always makes the 

 observed less than the true gradient. 



Observations in mines will be vitiated by the presence of pyrites, which 

 generates heat by its slow combustion, and are also liable to be vitiated by strong 

 currents of air ; but when they are taken at the newly-exposed face of a gallery 

 which is being driven into the rock, care being taken to prevent strong air-currents 

 at the place, and the surrounding ground not being too much honeycombed by 

 previous excavations, good results may be obtained. A hole should be bored to 

 the depth of about two feet in the newly-exposed face, the thermometer inserted, 

 and the hole very tightly plugged with clay. 



3. On the Botanical Affinities of the Carboniferous Sigillarice. 

 By W. C. Williamson, F.B.S., Professor of Botany in Owens College. 



The affinities of the Sigillarise are still in dispute. The English palteo-botanists, 

 apparently without exception, regard them as representing the highest modifications 

 of the Lycopodiacese. The French palaeontologists, and to some extent the 

 American ones, elevate them to the Gynmospermous group. The question is of 

 importance, both geologically and in reference to the problem of Evolution. 



The only plants associated with the Sigillarise in the Carboniferous forests, that 

 exhibit any possible affinities with them, are the Lepidodendra on the one hand, 

 and the Gymnospermous Dadoxylons and Cordaites on the other. Adopting the 

 processes by which we ascertain the affinities of any newly discovered plant, we 

 obtain results which appear to the author sufficiently conclusive. The old 

 idea that Sigillarise must have been large branchless stems must be abandoned. 

 Various examples, such as Lepidodendron Selaginoides, which the French palaeon- 

 tologists claim to be Sigillarian, branch like other Lepidodendra ; hence, whilst of 

 some forms the branches are yet unidentified, this branchless state is most probably 

 not a characteristic condition. Then the external leaf-scars of Sigillarise exhibit 

 nothing distinctive. Whilst in some types we have the vertical flutings of the 

 stem and the linearly disposed leaf-scars of the Syringodendra, typical examples, 

 such as Sigillaria de-gam and spinulosa, along with many others of Brongniart's 

 species, exhibit the diagonal arrangement of the leaf-scars characteristic of the 

 unquestioned Lepidodendra. Then no one ventures to doubt the absolute identity 

 of the cortical tissues in the two types of Lepidodendra and Sigillarise. It is 

 only when we reach the vascular axis that we find the supposed distinctions 

 upon which the French botanists rely. These distinctions rest wholly upon 

 the fact that, according to them, the Lepidodendra have a vascular axis in 

 which the scalariform vessels are not arranged in any radial order, nor increased in 

 bulk by any exogenous mode of growth, in the Sigillarise, whilst the central 

 part of the vascular area is occupied by a cylinder in all respects identical with 

 that of the Lepidodendra, it is surrounded by an outer zone in which the vascular 

 wedges are radially disposed, are separated by medullary rays, and have grown 

 exogenously through the operation of a cambium-layer. 



Whilst the author recognises the existence of these differences between the 

 Lepidodendron Harcourtii on the one hand, and the so-called Sigillarue, elegans and 

 spinulosa,^ on the other, he denies that such differences are even generic, much less' 

 ordinal, since in several cases they can be shown to be due solely to age. Three states 

 of Lepidodendron Selaginoides demonstrate this. In the one extreme form we 

 have the central non-exogenous vascular axis, giving off foliar bundles, but unens 

 closed by any exogenous zone. In the extreme opposite condition we find the 

 foliar vascular bundles apparently given off from the exterior of an exogenous zone 

 of the supposed Sigillarian type. In reality, these foliar bundles pass from the 

 inner cylinder through the outer one, but only appear conspicuously in transverse 

 sections at the exterior of this latter exogenous cylinder. 



But the author's cabinet contains intermediate examples, in which the stems 



