884 FOODS AND FOOD ADULTERANTS. 



used in the adulteration of teas. These illustrations were prepared 

 from photographic prints made by the following simple method. The 

 natural leaf was used in making an ordinary silver print, precisely as 

 the photographer would employ a negative. The finished print was 

 copied by a photoengraving process. Many of these illustrations show 

 even the delicate veins of the leaves; the tea leaf, however, is quite 

 fleshy, and did not yield a photographic print as distinct as those from 

 the other plants. The lower epidermis of the leaf contains most o the 

 stomata, which are surrounded by curved cells. There are few stomata 

 in the upper epidermis. The stomata are shown in Plate XLI. 

 Hairs are very numerous on the younger tea leaves, but sometimes 

 entirely wanting in old leaves. They always contain theine. Dr. 

 Thomas Taylor, 1 in a report to the Department, mentions the presence 

 of stone cells in tea leaves and states that his observations confirm 

 those of Blyth in regard to the absence of these formations in certain 

 leaves, viz, those of the willow, sloe, beech, Paraguay tea, ash, black 

 currants, two species of hawthorn, and raspberry. Dr. Taylor also 

 reports th e presence of stone cells in the leaves of the Camellia Japonica, 

 a plant related to the tea. Dr. Taylor prepares the sample of the leaf 

 for examination by boiling three minutes with a strong caustic soda or 

 potash solution. After the boiling a fragment of the leaf is placed on 

 a slide under a cover glass and the latter is pressed down firmly with a 

 sliding motion until the specimen is thin enough for microscopic exam- 

 ination. The stone cells appear as shown in Plate XLII. 



In the general study of the serration and venation of a tea leaf the 

 specimen should be steeped in hot water, and, after softening, the leaves 

 should be unrolled and spread upon a glass plate for examination by 

 transmitted light. Even small fragments of tea leaves will usually show 

 some distinctive characteristic. In general in may be stated that a 

 microscopic examination is only necessary in exceptional cases. In 

 doubtful samples the stomata should be examined, and a search should 

 be made for stone cells; the epidermis of both the upper and lower leaf 

 should be examined. Even in the case of dust the microscope will fur- 

 nish conclusive evidence as to whether it is from tea or some other 

 plant. 



According to Blyth 2 every part of a theine-producing plant, even the 

 minute hairs, contain this alkaloid. The writer cited employs the fol- 

 lowing method in examining a leaf fragment for theine: 



The leaf or fragment of a leaf is boiled for a minute in a watch glass with a very 

 little water, a portion of burnt magnesia of equal bulk is added, and the whole 

 heated to boiling and rapidly evaporated down to a large-sized drop. This drop is 

 transferred to a subliming cell, * * * and, if no crystalline sublimate be 

 obtained when heated to 110 (a temperature I'm above the subliming poiut of 

 theine), the fragment can not be that of a tea leaf. On the other hand, if a subli- 

 mate of theino in obtained it is not conclusive evidence of the presence of a tea leaf, 

 since other plants of the camellia tribe contain the alkaloid. 



1 Annual Report of the Secretary, 1889, p. 192. 



2 Foods: Their Composition and Analysis, A. W. Blyth, p. Hi'i'. 



