164 MISSOURI BOTANICAL GARDEN BULLETIN 
It is true that some of the commodities classified under 
plant products are made partly from animal and mineral 
products, but this is more than counterbalanced by the inci- 
dental plant products included under the animal and mineral 
classification. Our soaps are made from both animal and 
vegetable oils, but the latter play an important part, especially 
in the better grades. The chief vegetable oils used in soaps 
are those from the common cocoanut palm (Cocos nucifera), 
the oil palm (laeis quineensis), and the olive (Olea europaea). 
Our common food plants are so well known as hardly to de- 
serve mention. It may not be generally known, however, that 
macaroni is made from the glutinous flour of the hard or flint 
wheat (Triticum durum). Our rubber to-day comes from a 
number of plants, the most important being Hevea brasiliensis, 
the juice of which becomes Para rubber. The common rubber 
tree of houses and conservatories, Micus elastica, produces a 
relatively unimportant product known to the trade as Indian 
rubber. The chief ingredient of chewing gum is the coagulated 
juice of a Central American tree (Achras Sapota). This 
coagulated juice, or chicle as it is usually called, is also used 
in the making of statuettes. Living specimens of the oil palm, 
the olive, the cocoanut palm, the Para rubber tree, and the 
chicle tree may be seen at the Garden. 
TWIGS AS WEATHER RECORDERS 
Every tree is in a sense an automatic weather-recording 
instrument. Nearly every one has heard of the growth rings 
by means of which the age of a tree may be estimated and 
the growth of different seasons compared, but it is less com- 
monly known that many trees have scars left by bud scales 
on their smaller branches showing where growth started each 
spring. These disappear as the branch enlarges, but it is 
not at all unusual to find the complete records for the pre- 
vious ten to fifteen years. 
The amount of growth is determined by many factors, in- 
ternal and external, but a series of measurements recently 
made upon the silver maple trees of the Garden shows that 
climatie conditions have a surprisingly great effect. The an- 
nual growth in length for 1919-1922 was measured on ten 
