MICROSCOPE IN THE GARDEN. 41 



section of the brown outer coat of the common 

 onion is made, small prismatic crystals are observed. 

 These are represented at figure 72, plate 3. Some- 

 times several of these crystals unite together around 

 a central mass, forming a stellate body. These 

 bodies have been called " crystal glands," but they 

 have no glandular properties. They may be seen 

 in the root and leaf-stalk of common rhubarb, and 

 may be easily observed in a bit of rhubarb from a 

 spring tart. From such a source, the drawing was 

 made at figure 71. These crystals are mostly 

 formed of oxalate of lime. They are constantly 

 found in plants producing oxalic acid. The gritty 

 nature of rhubarb root arises from the presence of 

 oxalate of lime. Sometimes the oxalate of lime 

 assumes a round dish-like form. Such forms are 

 seen in plants belonging to the cactus family. A 

 circular crystalline mass, as seen in a common 

 cactus, is represented at figure 73. 



Other substances, besides oxalate of lime, are 

 found crystallized in the interior and on the surface 

 of plants. Crystals of sulphate of lime have been 

 found in the interior of cycadaceous plants. Car- 

 bonate of lime is found in crystals on the surface of 

 some species of Chara f or stonewort. There is a 

 shrub not uncommon in gardens, known by the 

 name of Deutzia scabra, on the under surface of 

 the leaves of which there are beautiful stellate 

 crystals of silica. The best way of seeing these ia 

 to put the leaf under the Microscope, and to 

 examine it by the aid of reflected light. 



Sugar and honey assume a crystalline form, and 

 may be known by the shape of their crystals. At 

 figure 238, plate 8, a crystal of honey is repre- 

 sented ; it is thinner and smaller than the crystal 

 of cane sugar represented at figure 239. Honey 

 is sometimes adulterated with sugar. Under these 



