OIL-DROPS, ETC. 223 



mount in water, and note the bright-looking oil- drops, 

 both in and about the section, and dispersed also in the 

 water. 



1. Irrigate with alcohol : the drops are not dissolved. 



If sections of the oily endosperm of Ricinus be treated thus, the 

 oil will be dissolved : this is characteristic of ethereal oils, but is 

 as a rule not the case with the fixed oils : to this the oil of Ricinus 

 is an exception. 



2. Treat a section with a considerable bulk of ether 

 in a watch-glass : wash with alcohol, and mount in 

 alcohol, or in glycerine : on examination the oil will be 

 found to have been dissolved by the ether. 



3. Stain a thin section with tincture of alkanet (see 

 Appendix A), the oil-globules stain pink. 



4. Treat a section with 1 per cent, solution of osmic 

 acid : the oil-drops will stain slowly, taking a dusky or 

 black hue. 



5. Treat a section with potash solution, and warm : 

 the oil will be partially and slowly saponified and 

 dissolved. This effect of potash is best seen in speci- 

 mens where the oil is present only in small quantities 

 as isolated globules. 



VI. Aleurone-grains. 



These are found of the largest size in oily seeds : they 

 vary somewhat in their characters in different plants : 

 those of Ricinus may be taken as a good type. 



Having noted the hard, variously marked testa, with 

 the wart-like swelling (aril) at the basal end, crack and 

 remove it: beneath it will be found the white oily 

 mass of the endosperm. Cut this through transversely, 

 and with a razor wetted with olive oil, or castor oil, 



