22 



COMPENDIUM OF GENERAL BOTANY. 



cell suspended in oil; the crystalloids are not visible because they 

 have the same refractive index as the oil. 



(/?) Globoids may be studied by first dissolving the aleuron and 

 eventually also the crystalloids by means of dilute potassium-hydrate 

 solution. The globoids are not soluble. According to Pfeffer they 

 consist of a double phosphate of lime and magnesia. The smallest 

 approach the limits of vision ; the largest are about 10/^ in dia- 

 meter. They are amorphous and isotropic, and hence produce na 

 polarizing light effects. 



{y) Crystals of calcium oxalate are usually found in such 

 aleuron-grains as contain no other inclusions. They are insoluble in 



A B 



Fig. 8. — Endosperm-cells of Ricinus communis. 

 A, as seen suspended in oil; B, ia potassium iodide-iodine solution, g, globoid; As, crystal- 

 loid. (After Frank.) 



dilute acetic acid. They usually occur in star-shaped clusters 

 (Krystalldrusen). 



The several inclusions are already formed before the develop- 

 ment of all the aleuron-grains, and are subsequently surrounded by 

 a deposit of aleuron. 



Protein crystalloids {a) not only occur in aleuron-grains, but 

 they are sometimes also found in the nucleus, frequently within 

 chromatophores (associated with an oily substance), and sometimes 

 in the cytoplasm or the cell-sap. 



(c) The Remaining solid dead Inchisions of the Cell. 



Fat-crystals seldom occur, although fats are plentifully distrib- 

 uted in the cell. This is because the plant-fats are liquefied at 

 ordinary temperatures and are therefore classed with the fatty oils 

 (page 24). Solid coloring substances are found here and there 



