40 A HALF-HOUR WITH THE 



through it ; so that by washing any vegetable tissue 

 containing starch, with water, and pouring it off 

 and allowing it to stand, the starch falls to the 

 bottom. This may be done by bruising the vege- 

 table tissue in a mortar, and then throwing it into 

 cold water. The tissue falls to the bottom, and 

 the starch is thus suspended in the water. In this 

 way the various kinds of starches may be procured 

 for microscopical examination. The granules of 

 starch have frequently a little black irregular spot 

 in their centre. In the starch of Indian corn it 

 assumes the form of a cross, which is seen at 

 figure 66, plate 3. Starch is a good object for 

 the use of the polarizing apparatus, which can be 

 applied to most compound Microscopes. The 

 grains of starch, under the influence of polarized 

 light, become coloured in a beautiful and peculiar 

 manner, permitting of great variation, as in the 

 case of all polarized objects. 



If we take a little of the white juice from the 

 common dandelion, and put it under the Micro- 

 scope, we shall often see, besides the globules of 

 caoutchouc which make the juice milky, crystals 

 of various forms. Such crystals are called by the 

 botanist " raphides," signifying their needle-like 

 form. They arise from the formation and accu- 

 mulation of insoluble salts in the fluids of the plant. 

 They are seen in various plants, and under very 

 different circumstances. Beautiful needle-like crys- 

 tals can be seen in the juice of the common hyacinth, 

 represented at figure 69 ; the juice may be ob- 

 tained by pressing. A question has been raised as 

 to whether they are always formed in the cell. They 

 are mostly found lying in the cell, as in the leavep 

 of the common aloe, seen at figure 70, plate 3 : 

 they may also be found in the tissues of the com- 

 mon squill, and in the root of the iris. If a thin 



