ON THE WOODY ZONE IN CALAMITE. 155 



the radiation thermometer placed at the same height above 

 the ground as the shaded maximum thermometer with 

 which it is compared ; but while freely exposed at all times 

 to direct sunlight^ it ought to be protected as much as 

 possible from disturbing influences. 



4. Solar-radiation observations made on a plan similar 

 to that adopted at Oxford show that the calorific intensity 

 of the sun^s light continued to diminish during the years 

 / 1865-66, when the frequency of solar spots was also 



diminishing, thus giving additional weight to the proba- 

 bility that changes in the heating power of the sun^s rays 

 are intimately connected with variations in solar-spot 

 frequency. 



X. On the Structure of the Woody Zone of an undescribed 

 form of Calamite. By W. C. Williamson, F.R.S., 

 Professor of Natural History in Owens College, 

 Manchester. 



Read November 3rd, 1868. 



Whilst engaged, some years ago, on an inquiry into the 

 nature of the fossil coal-plants known as Sternbergi(E, my 

 attention was arrested by some structures allied to those 

 found in Dadoxylon, but occurring in some stems of Cala- 

 mites. At the same time, the curious specimen repre- 

 sented in fig I, of which a woodcut w^as published in the 

 5th edition of ^Lyell's Manual of Geology^ (fig. 478), fell 

 into my hands, and threw new light upon the nature of 

 the small round cicatrices seen at the upper extremity of 

 the longitudinal ridges of each node in many Calamo- 

 dendra. These circumstances led me, in 1852, to prepare 

 numerous sections of these plants from the specimen in 

 my cabinet, represented in fig. 2, in which the structure 



