THE SOCIETY*S NOTE-BOOKS. 151 



fetua daidritica; the latter Demathim olivaceum. Dr. M. C. 

 Cooke believes it to be inorganic, and that it is caused by a speck 

 of Iron or Copper Pyrites in the paper. 



I have found it in considerable abundance in certain samples 

 of Blueisk-\\\\\iQ paper, and in a few cases, but much more 

 sparingly, on Cream-laid paper. I further suspect that its growth 

 is assisted by certain atmospheric conditions, such as dampness, 

 etc. In certain favourable circumstances, it not only penetrates 

 the sheet of paper in which the nucleus is found, but also 

 insinuates itself into the next sheets both above and below it. I 

 am inclined to think that this spot is only to be found on compa- 

 ratively modern-made papers, having searched carefully but 

 unsuccessfully through some old account-books that were used 

 before the days of steel pens. 



A. Allen. 



I have noticed these spots only on the blueish-white paper, 

 coloured with smalts, used for ledgers, etc. There can be little 

 doubt that they are merely inorganic, and due to crystallization. 

 The repetition of crystalline forms lying at similar angles to each 

 other will produce a very close imitation of vegetable forms, as all 

 may see on a frosted window-pane. 



Dendritic marks are common on the surfaces of the laminse of 

 certain rocks — as the Lias and Magnesian Limestone — and are 

 composed of oxide of manganese, or sulphide .of lead. 



H. Franklin Parsons. 



On rubbing the paper with a piece of India-rubber so as 

 partly to erase the Dendritic spot, it will be found to have spread. 



F. W. MORRISS. 



The above Notes were written three or four years ago ; but 

 within the last few weeks I saw at the printer's a quantity of 

 cuttings of blue-white foolscap paper, on which I found a number 

 of Dendritic Spots, some exceedingly minute, others very much 

 larger than any I had ever before noticed. Although I made 

 every enquiry, I was unable to learn the history of these cuttings, 

 further than that they were the waste trimmings of a job lately 

 executed. The paper was practically quite new, and I have every 

 reason to believe that it had left the mills at a comparatively 

 recent date, yet here were spots larger and more beautifully 



