104 PHARMACEUTICAL BOTANY 
CARBOXYLASE, found in higher plants, splits pyrotartaric 
acid into acetic aldehyde and carbon dioxide. 
C. Oxipizinc ENzyYMEs. 
These are enzymes which absorb molecular oxygen from the 
air and combine it with plant constituents. 
PEROXIDASE occurs in many plants including apples, many 
fleshy fungi, potatoes, etc. 
PEROXIDASES are common in plants and are responsible for 
discolorations seen in the tissues of many barks and fruits when 
they are bruised or broken and exposed to the air. The juices 
and extracts of plants containing oxidases turn brown upon 
exposure to air. This is owing to the formation of organic 
peroxides by the action of atmospheric oxygen on phenolic 
substances present and the presence of a peroxidase which, with 
an oxygen acceptor, brings about oxidation with a resulting 
colored oxidation product. 
25. Hormones.—The term “hormone” means chemical 
messenger and is appropriately named because it produces its 
effect at a distance from its point of origin. Hormones are 
substances which govern the proper development or functioning 
of organisms and organs. The hormones of animals, sometimes 
termed “internal secretions,” are formed by the endocrine 
glands as the pituitary, thyroid, parathyroid, adrenal, pineal, 
pancreas, ovaries, testes, and are secreted directly into the blood, 
lymph and cerebro-spinal fluid. 
The hormones of plants, while anticipated for some time, 
remained unknown until 1928, when F. W. Wendt demonstrated 
the existence of a plant growth hormone controlling the enlarge- 
ment of the coleoptile of the oat seedling. In 1933, F. Kégl 
and coworkers isolated 3 plant-growth hormones in crystalline 
form, auxin a (CisH3205) which they obtained from malt, maize 
germ oil and human urine, auxin b (CisH300,4) and hetero-auxin 
from vegetable material. Hetero-auxin has been identified as 
indole-3-acetic acid. Their formation and distribution has been 
found to be influenced by light. They regulate growth in plants. 
When seedlings are illuminated on one side, the growth 
hormone moves from the illuminated side to the shaded side. 
