164 THE AMEKICAN MONTHLY [July, 



than the average size of arrowroot grains. Grains of starch from differ- 

 ent plants vary in size from ^^^-q to ^^Vo of an inch. 



The polariscope will aid in the detection of starch in doubtful cases. 

 All varieties show a most characteristic cross in the centre, often called 

 St. Andrew's cross, and with a selenite plate a most beautiful object is 

 seen. The play of colors is wonderful. 



The largest starch grain is from the Carina edulls^ the root of which 

 is something like the potato. This starch may be procured under the 

 name of '' Tons les Mois " starch from Chas. W. Smiley, Washington, 

 D. C. If any should wish to send, ask for Walter White's preparation, 

 No. 170, an object well worthy of study. The grains of this starch are 

 so large and the markings so plain that a very low power vs^ill suffice, 

 while many other varieties require a high power to show them. 



To mount for the polariscope always use balsam or damar ; some 

 prefer benzol balsam, but be sure that the starch is dry or milkiness 

 will result. For the purpose of study always use some aqueous media, 

 as the balsam renders the grains so transparent that the resolution of the 

 markings is almost as difficult as to resolve Pleurosigma a7igulatum 

 in balsam by central light. Any of the aqueous media would preserve 

 the starch grains, but this is reliable : carbolic acid, six grains ; gly- 

 cerine, three drops. Mix and add distilled water, one ounce. If the 

 cells are properly, made and a plenty of gold size and cement is used 

 over the glass cover, there will be no difficulty about the mount keeping. 

 The following method of mounting arrowroot starch moving in fluid 

 is very valuable : Make a cell of four to seven layers of Brunswick black, 

 sealing-wax cement, or of King's lacquer cement in scarlet or blue. 

 Just fill the cell and no more with the above-named fluid. Put in almost 

 enough starch to cover the surface ; too much will defeat the object, too 

 little may not give a sufficient amount of weight to make the granules 

 roll. Cover and seal as usual. Do not forget to lay on a sufficient 

 number of layers of good cement with at least a day for each layer to 

 dry. The best plan in putting up fluid mounts is to begin the cell with 

 gold size and finish it with the same, whatever else you may use for 

 cement between these coats. 



When dry and you wish to see the motion of the granules under the 

 microscope set the slide on its edge for a short time to allow the starch 

 to settle on one side, reverse the slide on the stage, incline the stand at 

 least forty-five degrees, using a power not above one-half inch. The 

 field will be full of rolling spheroidal bodies, some of singular form, and 

 moving beautifully. They roll along from side to side, sometimes in a 

 mass, sometimes one alone will start and roll across the field striking 

 another granule, and one can imagine that he hears a clash as if two 

 stones had struck totjether. 



If when the slide is put on the stage the granules do not at once start 

 it will be sufficient to remove and lightly tap the edge on the table or 

 hand when on replacing tliey will be seen in motion. Those who have 

 never seen the starch under these conditions are strongly urged to try 

 this method. The arrowroot grain is the best adapted from the spheri- 

 cal shape of the grains. 



One caution : do not use too high a power, as one of one-half, three- 

 fourths, or one inch is far better than higher, as the structure is made 

 out and a larger field is obtained in which to watch the movements. 



