THE AMERICAN BOTANIST 13 



those of the mint and geranium. The plant acids also belong 

 to this group. Acids are usually retained in the plant, and yet, 

 not being in the general protoplasm and not in the seat of 

 activity, are said to be secreted rather than excreted and are 

 therefore waste to the plant. The oils in the orange and lemon 

 are secreted in specialized glands well down in the epidermis, 

 while the acids accumulate in the pulp outside of the seed 

 vessels and away from the growing seed. Just as citric acid is 

 accumulated in lemons, oranges, and allied fruits, so are oxalic 

 and malic acid in apples and pears, and tartaric acid in the juice 

 of grapes. In this group, we find alcohol obtained by fermenta- 

 tion resulting from the action of enzymes on the acids and 

 sugars. Tea is the watery extracts of tannin from the tea leaf. 

 These substances are waste products as far as the plant is con- 

 cerned. They have no nutritive value to the plant ; in fact are 

 often poisonous. 



Milky juices are very common excretions from plants. The 

 Milkweed family is distinguished by a milky fluid which is 

 stored in its vessels and exudes when cut or crushed. Upon 

 exposure to the air this milky latex coagulates and forms, upon 

 drying, a sticky, elastic mass which, in some plants is sufnc- 

 inently abundant to furnish the India rubber of commerce. 

 The rubber tree is a very large tree somewhat like the Eng'lish 

 ash and grows to a height of 00 feet. They are never found 

 in groups. \\ hen a tree is about 20 years old, it is tapped. The 

 tapping is done from the ground as high up as a man can reach 

 and sometimes higher. This hole is not bored with an auger 

 as in the tapping of the maple trees, but gashed with a hatchet 

 just deep enough to cut the bark but not the wood. As the 

 rubber gatherer draws out the hatchet a milky white fluid oozes 

 forth. The tapper then inserts a little cup below the gash, 

 fitting it by a slight cut in the bark. He makes at least three 

 such cuts in each tree. Since these trees grow far apart the 

 tapper must cover a great deal of ground in his daily work. 



