1892.] THE MICROSCOPE. 227 



117. Are not sections usually ctit too thin? Is not a ivedge- 

 shaped sectiofi advisable? I use a binocular and argzie thick 

 sections. 



A thin section is best for use with high powers, for the study 

 of individual cells and other minute details. A thick section is 

 useful for the study of the relation of cells, vessels, etc., with 

 moderate powers. 



Judgment should be exhibited in the cutting ; some material 

 should be cut rather thick but in general a thin section is best 

 for real study. A wedge-shaped section might have the thicker 

 portion wrongly placed. A binocular microscope is good enough 

 for pretty views of sand, foraminifera, etc., but not for critical 

 study on sections or anything else. 



118. Do similar inoulds grow on allied fruits., like the peach 

 and phcni? 



Moulds are lowly plants, and some species seem, at times, to 

 run into others. Their presence depends upon favorable condi- 

 tions of atmosphere and nutrient surface, but the rule is for each 

 species to find a certain fruit or leaf more favorable for its devel-- 

 opment, more especially if accident or disease has weakened the 

 vitality of the host plant. 



119. Do varieties of one _fa?nily of plants produce similar 

 pollens ? 



The pollens of one family are similar, but may vary greatly in 



size. 



120. What is the best method for preparing Herapath crys- 

 tals for the polariscope ? — B . 



Take of acetic acid, 30 drops ; alcohol, 10 drops ; dilute sul- 

 phuric acid, I drop ; mix. Place a drop of this on a glass slip ; 

 add a crystal of quinine sulphate ; when dissolved, add a minute 

 drop of tincture of iodine ; set aside, protected from the dust ; 

 crystals will form slowly. When the crystals are dry, add a drop 

 of balsam, and cover. This process will produce a small nest of 

 small crystals. The preparation of large crystals is a tedious 

 and troublesome process (see Micrographic Dictionary, 4th 

 edition, page 650). 



121. In rearing Der?nestes, I noticed parasitic mites on 

 some of them. I have them preserved i7i alcohol. What is 

 the best method for mounting 77iites ? 



Transfer the mites from alcohol to glycerine and water ; after 

 a day or tw^o, mount them in glycerine or Farrant's solution, or 

 transfer them from alcohol to oil of cloves, and thence to a drop 

 of balsam on a slip and cover. 



