VARIOUS STARCHES. 17 



vary in thickness, it is advisable to raise the tube of the micro- 

 scope before placing under it a new preparation, though this is 

 not, of course, necessary when using a low power. 



As the first preparation will be required again, sve place it in a 

 large moist chamber. This moist chamber consists in a deep 

 plate (e.g., soup plate) and a bell-glass (or cloche) with knob. On 

 the plate stands a zinc frame, such as is described and figured in 

 the Introduction (Fig. 1), and water is poured into the plate till 

 the bell- shade has its lower edge quite immersed. 1 The prepara- 

 tion is laid upon the frame. Before this, however, we make sure 

 that the drop of water under the cover-glass of the preparation is 

 not already partially dry. If this should happen, we place a small 

 drop of water on the slide at the edge of the cover-glass, so that 

 it may be sucked in by capillarity. We also mark the slide, pre- 

 ferably with one of Faber's coloured pencils which write on glass, 

 or upon a scrap of gum-paper attached to the slide, so that the 

 preparation may not afterwards be confused with others. 



Upon examination of the new preparation we shall find that 

 the lamination of the starch which has been preserved air-dry is 

 at least as clear as in the fresh grains. This preparation also we 

 place in the moist chamber. 



Bean Starch. Now make a preparation of air-dry bean flour 

 (Phaseolus vulgaris). The grains (Fig. 6) examined in water 

 appear oval or circular; they 

 are slightly flattened; a certain 

 medium size predominates. The 

 lamination is very clear and 

 very uniform ; the lamellae show 

 a well-nigh equal thickness. The 

 hilum is central, and the struc- 

 ture concentric. The hilum of 

 grains examined in water is hollowed, more isodiametric in the 

 rounded, and elongated in the oval forms. From this hollow 

 extend radial clefts, which cut through the layers at right angles, 

 and, thinning off, reach almost to the periphery of the grain. 



Now lay a trace of this bean flour in pure glycerine instead of 



1 This last precaution (immersion of the rim) is not so essential in the 

 relatively moist air of an English room or laboratory. It is most convenient 

 to use a soup-plate with regular rim, on which the bell-jar rests closely, and 

 pour water into the bottom of the plate. If the preparation has to be kept 

 for many hours, greater precautions against drying may be needed. [ED.] 



2 



