30 COMMERCIAL SICILIAN SUMAC. 



The under epidermis cells (PL II, fig. 2) have not quite so promi- 

 nent walls as those of the upper layer and the outline is more inclined 

 to be wavy. The limits of variation in diameter also exceed those 

 of the upper surface. From six to ten cells are radially grouped 

 around each stoma. In the ordinary clearing process these cells, 

 together with the stomata, commonly clear up more perfectly than 

 the rest of the epidermal cells, thus giving to the specimen when 

 viewed under the microscope with the objective slightly out of per- 

 fect focus a mottled appearance which is very characteristic. 



TAMARISK (Tamarix africana). 



This material cleared in chloral hydrate is more brownish in color 

 than the species previously mentioned. The most characteristic 

 feature observed is a papillae-like appearance on the surface of the 

 leaves distinguishing it from the other plants studied. This is best 

 observed on fragments which lie partially on edge, in which position 

 the little protuberances are readily seen. (PI. Ill, fig. 1.) 



SMOOTH SUMAC (Rhus glabra). 



Though this species is not very commonly found if at all in Rhus 

 coriaria as imported into this country, it is one of the possible adul- 

 terants that should be kept in mind. On neither surface of the leaf 

 are the horn-like trichomes present. The cells on the upper epider- 

 mis resemble those on the upper epidermis of the It. coriaria, being 

 ordinarily from 25/f to 52/* across. The beaded cell walls noted in 

 the case of the E. coriaria are very pronounced in the R. glabra (PI. 

 Ill, fig. 2), and, together with the absence of trichomes, have been 

 used as the basis of its identification. 



The under surface of the leaf has epidermal cells and stomata and 

 glandular hairs very much like the R. coriaria, but the cell walls do 

 not generally show quite so much undulation. The fact that the 

 horn-like trichomes are absent from both sides of the leaf is of addi- 

 tional service in the identification of whole or rather coarsely ground 

 material, but in very finely ground samples can not be relied upon 

 with certainty. 



CHEMICAL DETERMINATION OF ADULTERANTS, 



In the detection of adulterants it is customary to place depend- 

 ence only on the microscopical examination of the sample, no chemi- 

 cal tests being regarded as of practical value for this purpose, although 

 Proctor a states that any sumac infusion rendered turbid by bromin 

 water is open to grave suspicions. Work in this laboratory has 

 shown that while pure sumacs are not as easily precipitated, requir- 

 ing more bromin water than lentiscus extracts do, both the sumac 



a Principles of Leather Manufacture, 1903, p. 272. 

 117 



