208 BOTANICAL MICROTECHNIQUE. 



caustic potash solution, as well as in hydrochloric acid of 

 various strengths. But it is not attacked by the above- 

 mentioned digesting fluid, even after lying in it for days. 

 Hcematoxylin and Congo red are specially adapted to 

 staining the envelope. By the combination of safranin and 

 haematoxylin, Hieronymus obtained preparations in which 

 the envelope was stained violet and the crystalloid deep 

 red. 



d. Oil-drops. 



364. Drops of an oil-like substance are pretty widely 

 distributed within chromatophores, as has been shown 

 especially by A. Meyer (II), and Schimper (III, 106). Ac- 

 cording to A. Meyer's researches (II. 17), however, these do 

 not fully correspond in their chemical relations either with 

 the true fatty oils or with the ethereal oils. It is especially 

 noteworthy that they are soluble even in dilute alcohol, but 

 insoluble in acetic acid. They are, further, only very grad- 

 ually browned by osmic acid, and are always insoluble in 

 water, but readily soluble in ether. They behave variously 

 with chloral hydrate. According to all these reactions, the 

 bodies in question must surely be nearly related to the 

 fatty oils, so much the more that they stain deeply with 

 alcannin and cyanin by the use of the methods previously 

 described ( 109, 1 10). At all events, it seems to me best 

 to designate these bodies as oil-drops, as has usually been 

 done in the literature, so long as no exact investigations of 

 them exist. 



I can recommend as a suitable object for the study of the 

 reactions of these oil-drops, the epidermis of 

 the leaf of Agave americana. This contains 

 leucoplasts which always enclose pretty large 

 oil-drops, especially in old leaves (cf. Fig. 44). 

 In yellowed leaves these have usually run 

 together into a single large drop, beside which 



FIG. 44. Leuco- 



plasts from the the rest of the leucoplast is so inconspicuous 



epidermis of an 



adult leaf of th a t ft cannot usually be directly made out 



Agave amertca.- 



na. o, oil-drops. w Jth certainty, by direct observation. 

 The oil-drops observed in the chromatophores of older 



