CORRESPONDENCE. 191 



genera. You may make gathering after gathering in your own neigli- 

 boiu'hoocl, but though you may make a large collection of material, 

 which you could not use up in your lifetime, your gatherings would 

 very likely contain but multitudinous repetitions of the same class of 

 diatoms. It would probably be the same with, the gatherings you 

 might make in your sea-side trips, and still more probably so in your 

 pi-ejiarations of guanos from diiferent localities. The consequence is 

 that you would in all likelihood get tii-ed of making gatherings, and 

 having the trouble of preparing and cleaning them. 



Diatomaceoiis material, either prepared or unprepared, cannot, as 

 far as I am aware, be bought unmounted, whether it be of British or 

 foreign genera ; and the present mode of exchanges amongst amateurs, 

 carried out through the exchange columns of different journals, is 

 unsatisfactory in the extreme, as one can never know what kind of 

 rubbish ho may have sent him in the way of barter. 



The professional preparers will not sell material in even the 

 smallest quantities. It seems almost incredible, but let the following 

 statement, which I vouch for as fact, speak for itself, and you will 

 see, that though to prepare a mixed slide for the market the preparer 

 has to put a certain sized dip of material on a glass slide and evapo- 

 rate it, if you ask him to stop the j)rocess there, and sell you that 

 slide for a shilling — the same price, mind you, that he will ask for it 

 when it is completely mounted and ready for the market — he will not 

 sell it you. No ! He will cover it with Canada balsam and a glass, 

 he will clean off the superfluous material, and perhaj)s take the trouble 

 of putting on a ring of cement, and when he has thus spoilt it for the 

 piu'poses for which you want it, he ^\'ill offer it you for a shilling. 

 This is precisely what happened to me. I offered to a well-known 

 preparer of microscoj)ic objects, whose name I will not mention, a 

 shilling a-piece for a single dip — the ordinary quantity put on a slide 

 — each of certain deposits from which I wanted to select forms myself 

 for my own cabinet, and he refused to let me have them. I thought I 

 should succeed in my object by ordering some of these preparations 

 mounted dry, and by melting the cement and removing the cover I 

 could get what I wanted. But do you think I was allowed to have 

 them ? No ! It is usual to mount them in balsam, and in balsam I 

 must take them, or go without. There is a certain class of diatoms 

 only, that the mounters put up dry for the market, and fi-om these only 

 are you allowed to select. Foiled in my fii-st attempt, I made apjjli- 

 cation to another equally well-known mounter, and I should like to 

 publish his name, because he did at any rate write me a very civil 

 letter in reply, showing me that it was not his fault that he could not 

 comply with my request, but as I have not his authority to do so, and 

 he might not like it, I refrain from doing so ; but I give the text of 

 his letter, as I think it may be interesting. He says : — • 



" Sir, — I beg to assure you that I have not forgotten or neglected 

 to notice your letter of the 14th instant, but have given to it frequent 

 thought. I regret that I cannot comply with your \vish, from various 

 causes. Many of those diatoms are not my own mounting, and those 

 who have the material woidd not listen to your wishes, I am sure, 



