Algae 



FLUID WHOLEMOUNTS — AQUEOUS TYPE 



27 



the cell with it. Particular attention 

 should be paid to the junction of the cell 

 with the slide, whore tnipi)ed air bubbles 

 are often caught. The author finds it 

 best not to lower the coverslip horizon- 

 tally, as in the previous mount, but to 

 shde the cover horizontally onto the cell. 

 This is shown in Fig. 16 where the cover- 

 slip has reached halfway across. This 

 illustration is shghtly exaggerated since 

 the cover may be started farther across 

 and sUd only the last few miUimeters. 

 Care must naturalh' be taken that the 

 gold-size protective ring is sufficiently 

 dry not to smear the coversUp as it is 

 pushed. If, when the cover reaches nearly 

 to the other side of the cell, a small air 

 pocket is left, it may be filled with moun- 

 tant and the coverslip pushed neatly into 

 place. It is also possible to lower the 

 coverslip from one side — that is, to place 

 one edge in contact with one edge of the 

 cell and to lower the other with a needle — 

 provided that object is sufficiently large 

 not to become displaced. 



Fig. 17 shows the covershp in place 

 after it has been pressed in contact with 

 the protective ring and after the mounting 

 fluid has been wiped from the outside. 

 This is more difficult, and must be done 



more carefully, than in the case of the 

 flat mount previously discussed. A ring 

 of the first sealing cement is then (Fig. 

 18) applied to fill the gap between the 

 ovcrliip of the coverslip and the protective 

 ring on the inner edge of the cell. It is 

 not necessary to do this on a turntable 

 since this cement need not come onto the 

 top of the coverslip at all but may be 

 applied directly from the side. After this 

 cement has had time to dry one should 

 then build up (Fig. 19) several layers of 

 asphalt varnish. So many laj^ers are re- 

 quired to fill the angle between the cell 

 and the coversUp that it is often desirable 

 to use some cement containing a pigment. 

 If a pigmented cement is used it should, 

 however, be given a coat of waterproof 

 asphalt varnish on the top before the slide 

 can be considered finished. The purpose of 

 a thick layer of cement, filling the angle 

 between the cell and the slide, is to pro- 

 vide additional mechanical support to the 

 cell. The most frequent cause of break- 

 down of thick aqueous mounts is either 

 the complete detachment of the cell from 

 the slide, or the cracking of the ce- 

 ment which holds the cell in place with 

 the subsequent intrusion of small air 

 bubbles. 



Specific Examples 



Preparation of a Wholemount of Microcystis in the Fluid of Ripart 



AND Petit 1884 



Wholemounts of unicellular algae pre- 

 pared in any medium except balsam are 

 rarely seen nowadays. These balsam 

 mounts, though they display fairly clearly 

 the internal structure of the alga, give 

 the student not the faintest idea of wdiat 

 the material looks like in life. Nothing is 

 more valuable for the laboratory instruc- 

 tion of classes, who will subsequently 

 study in the field, than a series of whole- 

 mounts of phytoplankton preserved so as 

 to resemble, as nearly as possible, the Uving 

 material. It is the author's opinion that 

 the solution of Ripart and Petit, used as 

 described in this example, gives as close an 

 approximation to the appearance of the 

 Uving material as can be produced. Very 

 weak solutions of formaldehyde are often 

 used for the preservation of vials of 



phytoplankton concentrates for labora- 

 tory study, but it is not, in the writer's 

 opinion, a satisfactory medium for the 

 preparation of a wholemount. 



The blue-green alga microcystis has 

 been selected for the present example 

 because it hajjpens to be the most common 

 alga found in large bodies of w^ater in the 

 district from which the author is writing. 

 Other blue-green and green algae may 

 just as well be prepared by the present 

 method. It is a waste of time to endeavor 

 to concentrate algal collections in the 

 field. Several gallons of the greenish 

 water containing these specimens should 

 be collected and brought back to the 

 laboratory for immediate processing. 



There are two ways of concentrating 

 the specimens. The first is to add to the 



