i 4 2 SCIENCE PROGRESS 



are Weiss's paper (69) on the tyloses occurring in the stem 

 of Rachiopteris comigata, and Watson's communication (65) on 

 Cyathotrachus alius, an isolated sporangium from the Lower 

 Coal Measures. 



Kidston {$6) has briefly described a new Botryopteris and 

 a section of an interesting fern of the genus Dineuron, from 

 the Lower Carboniferous of Pettycur (Burntisland). Gordon 

 has in preparation memoirs on Dineuron and other remarkable 

 genera from the same locality. 



The Cordaitales 



Scarcely any research has recently been attempted in 

 Britain on this important group. The last memoir of special 

 interest is that by Scott (44), " On the primary structure of 

 certain Palaeozoic stems with the Dadoxylon type of wood," 

 published in 1902. Since then apparently only one other paper 

 has appeared, founded on French Stephanian material, in which 

 Miss Stopes (59) described the leaf structure of Cordaites. We 

 await with interest the researches of Scott and Maslen on the 

 genus Poroxylon, and of Miss Robertson on the seed Ccirdio- 

 carpon. It is also much to be desired that further work on 

 British specimens of this group should be undertaken, especially 

 as regards the fructifications, if by any chance the material can 

 be obtained. 



The Origin of Plant Petrifactions 



Within the last decade, the nature and origin of the 

 calcareous nodules, known as coal balls, in which petrified 

 plant-remains occur in the Lower Coal Measures of England, 

 has been the subject of inquiry at the hands of Stocks (58) 

 and more recently of Stopes and Watson (62, 63). Stocks 

 studied the precipitation of calcium carbonate from solution 

 in the presence of organic matter and concluded that the 

 carbonate of the coal balls " first separated in the cells of 

 waterlogged vegetable matter and then around it, forming a 

 concretion which grew in the bacterial jelly, and hence 

 acquired its rounded shape." The bacterial jelly was formed 

 by the anaerobic decay of vegetable debris in stagnant sea- 

 water brought about by bacteria. 



Stopes and Watson find that "the coal balls were formed 



