Chromosomes 



SQUASH PREPARATIONS FROM SOLID BODIES 



77 



the products of maceration present many 

 difficulties. It' the preparation is broken up 

 under a covershp, it is difficult to remove 

 it witliout losing the cells, or to stain them 

 with the coverslip in place; if the macera- 

 tion is carried out in a small tube, it is 

 difficult to concentrate the cells readily on 

 the slide after they have been stained. 

 Probably the simplest method in most 

 cases is to treat the individual cells as 

 though they were a culture of protozoans: 

 that is, to stain them, dehydrate them, 

 and get them into a small quantity of 

 balsam, and then to place a drop of this 

 balsam under the coverslip. As an alterna- 

 tive to this, the macerated material may 



1)6 smeared over the surface of a slide 

 which has had an adhesive applied to it, 

 or it ma}' be diluted with an adhesive 

 material such as Mayer's albumen and 

 then treated as though it were a fluid 

 smear. The ol)jection to this treatment is 

 that the majority of fixed cells are very 

 brittle and will be damaged when the 

 smear is made. 



The selection of a stain is not difficult 

 since each dissociated cell may be treated 

 as a small wholemount. It is not worth 

 while to double-stain macerated speci- 

 mens, the true function of which is to 

 present a clear picture of the shape, not 

 the nature, of individual cells. 



Typical Examples 



Preparation of Microsporocytes of Crocus for Chromosome Examination 



In the last chapter it was pointed out 

 that material of this nature could be 

 squeezed from the anther and spread over 

 a sfide with the back of a scalpel. This 

 method inevitably leads to distortion both 

 of the cells and of the chromosomes, and 

 in the writer's opinion the method here de- 

 scribed gives a better preparation. There 

 is first the collection and fixation of the 

 anthers, and second, the separation of the 

 microsporocj'tes from the other cells of the 

 anther by maceration. 



The advantage of the crocus for this 

 jDreparation is that it maj^ be brought into 

 flower in the laboratory at any season of 

 the year. The anthers may be taken at 

 any stage of their development, the most 

 useful stage for demonstration prepara- 

 tions being that which is reached when 

 the flower is just beginning to color. The 

 flower is removed from the corm, the 

 petals stripped away, and the anthers 

 placed in fixative. Many fixatives may be 

 used, though one of the best is Navashin 

 (Chapter 18, F 6000.1010 Navashin 1912). 

 The anthei's are placed in several hundred 

 times their own volume of this fluid which 

 is, by convention, but probal^ly unneces- 

 sarily, kept in the icebox. The anthers are 

 removed after 24 hours and waslicd over- 

 night in running water. 



The method of maceration selected for 

 this example is that of Faberge 1945; the 

 abbre\aated directions are in Chapter 19 

 under the heading V 41.1. This method 



uses the stomach of the edible snail {Helix 

 pomatia) which dissolves the intei'stitial 

 tissue of plant cells. Edible snails are ol)- 

 tainable either by collection in the field o r 

 from restaurant supply houses. Snails ob- 

 tained from the latter are usually in a state 

 of liibernation from having been kept on 

 ice and must be revived by being kept at 

 room temperature for a day or two, after 

 which they may be given a meal of lettuce 

 and used on the day following. The snails 

 are killed by drowning in warm water 

 overnight, which leaves them fully ex- 

 panded, and the stomach is then dissected 

 out. The snail is removed from the shell 

 and pinned down through the foot. The 

 mantle cavity is then lifted in a pair of 

 forceps and sfit. As soon as the edges of 

 this sfit have been pulled back the crop 

 (often miscalled the stomach) will be seen 

 as a carrot-shaped body filled with brown- 

 ish fluid. The fluid within the crop must 

 now be withdrawn, either by the insertion 

 of a hypodermic syringe, or by figaturing 

 the crop at each end, removing it, and then 

 squeezing the contents into a tube. It is 

 simplest to handle a good many snails at 

 the same time, since the material removed 

 may be preserved in an icebox with a drop 

 of toluene on top. 



The anthers, taken either from the 

 water in which they have been washed or 

 the alcohol in which they are stored, are 

 placed in a drop or two of the enzyme solu- 

 tion. If the maximum number of sfides 



