72 CELL-CONTENTS AND CELL-WALLS. 



For instance, the glucoside amygdalin occurs in Almonds, 

 and is obtained by extraction with alcohol and precipita- 

 tion with ether. The enzyme eniulsiii (found in germi- 

 nating Bitter Almond seeds, also in the leaves of Cherry 

 Laurel, Bird Cherry, etc.) decomposes amygdalin into 

 prussic acid, benzaldehyde, and glucose. Salicin, found 

 in the twigs of Willows and Poplars, and obtainable in 

 the same way, is converted by emulsin into glucose and 

 saligenol (salicylic alcohol). 



(a) Examine commercial salicin ; note its bitter taste. Dissolve 

 some salicin in warm water, and note that (1) it does not reduce 

 Fehling's solution ; (2) it gives a red colour on addition of strong 

 sulphuric acid if water be then added, a red precipitate is given ; 

 (3) it gives no colour on addition of dilute ferric chloride solution. 



(&) Using a Soxhlet fat- ex traction apparatus ( 97), extract sali- 

 cin from some chopped-up twigs of Willow or Poplar with water. 

 Test the watery extract as in the preceding experiment. 



(c) Add dilute sulphuric acid to some salicin solution, and boil. 

 Neutralise with caustic soda, and apply Fehling's test a reducing 

 sugar is now present. 



(d) Grind up some Bitter Almonds in a mortar with sand and 

 water. Filter the liquid, which will contain emulsin. To salicin 

 solution in test-tubes add (A) some of the emulsin solution ; (B) 

 some emulsin solution that has been boiled ; (c) some diastase 

 solution ; leave (D) with nothing added to the salicin solution. 

 Place the tubes on a bath at 40 C. for half an hour or an hour. 

 Test with Fehling's solution : glucose is present in A, though absent 

 in the other cases. Note that in A the addition of some dilute 

 ferric chloride gives a deep purple colour (destroyed by acids or by 

 alkalis) ; this is due to the presence of saligenol. 



(e) Grind up in the same way some Sweet Almond seeds, and 

 note that the watery extract in this case contains emulsin, but 

 there is no amygdalin. To some of the extract of Bitter Almond 

 seeds, which has been boiled so as to destroy the emulsin present in 

 it, add some of the Sweet Almond extract, and note that hydroly- 

 sis occurs glucose, prussic acid, and benzaldehyde (oil of Bitter 

 Almond) being formed. 



(/) In transverse sections of the leaf of Cherry Laurel note that 

 there is a layer of cells surrounding the vascular bundles, marked 

 by the finely granular character of their protoplasm and their free- 

 dom from chloroplasts and starch. (1) Apply the tests for tannin 

 ( 84) to some sections these cells contain tannin. (2) Treat 

 sections with Millon's reagent on warming the slide, note that 

 these cells turn deep orange red, while the ordinary parenchyma 



