1889.] MICKOSCOPICAL JOURNAL. 77 



power, however, for the desmids are mostly small objects, ranging in 

 diameter from gVth inch in the larger forms oi ^licrasterias to j^j^fth 

 inch in the smaller species of Closterium. The length varies between 

 Jpth inch {Docidiit/n) and TjoTrth inch {Sta?frasirtim) . The average 

 diameter is not more than a^Tnith inch, probably less. A ^th, 4th. or 

 even ^th objective will be needed at times. And to use these with the 

 binocular you must have fairly wide-angled objectives, and the Abbe 

 condenser, the binocular diaphragm, and the flat-wick lamp turned 

 broadside to the condenser without the mirror. It is well to use the 

 Hopkins' light modifier also — the pale blue tint. By these means I 

 get both fields perfectly lighted with the ^th of 85° Crouch, and the 

 \\\v of 125° Bausch & Lomb, and well enough lighted with eve7i the 

 ^th homogeneous immersion of same make to view^ any object in the 

 centre. The dark bands appear on the sides of the field, but occasion 

 no real difficulty. 



To those who have never used the binocular with such powers on the 

 desmids, the very first trial will be a revelation, and I am confident they 

 will employ it ever after in their examination of these forms. At a meet- 

 ing of the Roy. Mic. Soc. of London some years ago, Mr. Beck said 

 he " remembered that when his brother Richard showed Aulacodiscus 

 to Mr. Tuflen West for the first time under the binocular, that distin- 

 guished draughtsman looked at it for some time in silence and then 

 jumping up exclaimed : ' all the drawings oi Diatomacece which I have 

 done will have to be done over again !' "* And that is the feeling one 

 will have after applying the double tube to Etiastrum or Staurastrmn., 

 for example, — all his slides of desmids will have to be examined over 

 again. 



COLLECTING. 



But here I am reminded of the old recipe for rabbit stew, " First catch 

 your hare." Before one can examine the desmids he must first gather 

 and mount them. A few words, therefore, about their collection and 

 preservation are necessary in such a paper as this. The best places for 

 desmids, from my experience, are small, shallow pools and ditches, 

 and the best outfit is the simplest possible, — a wide-necked bottle and a 

 coffee strainer some 3 inches in diameter, with a fine mesh, ^^j^^th inch or 

 less. These, with a cane or a jointed rod (a Japanese fishing pole cost- 

 ing a trifle will do), are positively all you need. For the small pools 

 the strainer alone is sufficient ; for the larger it can be fastened by its 

 handle and tw^o pieces of string or tape to the cane or rod. The advan- 

 tage of this simple outfit is that you W\\\ often take it when tomato cans, 

 etc., which are recommended, vjotild be left behind. The desmids 

 are said to be free ffoating, but I have had far better success with the 

 superficial ooze on the bottom than WMth the water at the surface. Skim 

 the ooze gently with the coffee strainer and pour -into the bottle, repeat- 

 ing till it is full. After the stuff' has setded pour off" most of the water 

 and refill. If there are any desmids in the pool, pond, or ditch, you 

 will be sure to have a good gathering by this means. Don't slight any 

 pool or ditch because it is small or shallow. The best gathering of 

 Euastrum I ever made was from a pool not more than four feet in di- 

 ameter and six inches deep, while one about twelve feet across and a 



* Amer. Mon. Mic. Jour., June, 1883. 



