276 CONTENTS AND PRODUCTS OF CELLS 



a thin cross-section of the peripheral cells of a grain of wheat 

 and mount in alcohol. Stain with an alcoholic solution of 

 iodin to color the grains yellow, and examine with the high- 

 est power. Make a sketch of a few layers of cells, just be- 

 neath the epidermis. Make a sketch of a few of the grains 

 removed from the cells. While looking at the mount, run a 

 little water under the cover-glass and watch the result. 

 Make a similar mount and study of the endo- 

 sperm of castor-oil seed, or of grape seed. In 

 the castor-oil seed, look for inclusions of large 

 crystaloids and small globoids. In the grape 

 seed, globoids should be found with crystals of 

 calcium oxalate within tHem. This experi- 446 Raphideg of 

 ment will require the power of one-sixth or rhizome of skunk 

 one-fifth inch objective. 



467. Cells may contain crystals. Besides the crystals 

 found as inclusions of aleurone grains, many others occur. 

 In onion skin they are prisms; in nightshade they are in 

 the form of crystal flour; in the petioles of the peach they 

 are roundish, with many projecting angles; in the root-stock 

 of skunk cabbage, in the bulbs of hyacinth, and leaves of 

 tradescantia they are needle-shaped and are called raphides. 

 (Fig. 446.) In the leaf of the India-rubber plant (common 

 in greenhouses) are found compound clusters resembling 



bunches of grapes, which are called cysto- 

 liths. (Fig. 447.) These are concretions and 

 not true crystals. In saxifrage, mineral 

 matter appears as incrustations on the sur- 

 face of the plant. Toward autumn, crystals 

 of calcium oxalate become very abundant in 

 447. Cystoiith in leaf the leaves of many deciduous trees; examine 

 of rubber plant.— cr0 ss-sections of peach petiole in June and 



Ficus elastica. c r 



again in October. 



468. To study crystals and cystoliths: Section the root- 

 stock of skunk cabbage or Jack-in-the-pulpit, the leaf 



