fxS Transactions of the Academy of Science of St. Louis 
industry. In other words, the situation might have been ahnost 
hopeless from the standpoint of the forest conservationist. It is 
quite otherwise. 
Some of the war time uses for wood may be of interest. 
The earher airplanes had wood frames, but for many years 
aluminum has been the material most used. The British, how- 
ever, early in the war turned to spruce for their fighter planes 
I 
because of the shortage of alumnium. More recently our own 
engineers have done likewise. The favored Sitka spruce is quite 
limited and the result has been the practical exhaustion of this 
valued material and the necessity of turning to noble fir, western 
hemlock, yellow poplar and maple. A somewhat similar substi- 
tion of interest to us is that of Douglas fir and southern pine for 
the decking of war vessels, in place of the favored teak. The 
latter comes from India and the war has cut off the supply. 
Pontoon bridges for the army engineers are being built of 
wood in place of the light metals, both because of the shortage 
of the latter, and because wood has certain advantages. Repairs 
at the front are more readily made and when such bridges are 
broken up by shell fire, the floating wood parts provide something 
to which the boys may cling. 
An interesting development has been the use of steel grids 
to transform beaches or other flat areas Into landing fields within 
a few hours. It has been found that rubber tires of air craft are 
on these steel grids. 
This has resulted in the production of wheels of laminated hard- 
wood, which wear much longer. 
Within the last decade or so, what are known as timber 
connectors have come into rather wide use. These are steel rings, 
or toothed grids, which are inserted between the wood sticks of 
a truss or framework to form, with the bolts, a very much 
stronger joint than can be obtained with bolts alone. As the 
joint is usually the limiting feature in the design of a timber 
structure, these connectors permit equally strong contsruction 
with considerably smaller pieces of wood. Unfortunately, from 
the timber conservation standpoint, this type of wood construc- 
tion Is so efficient, that we see it used for many large structures 
to replace steel where otherwise only steel would have been pos- 
sible of use. For example, some hangars for dirigible air craft 
have been constructed using wooden roof trusses and frames 
^^irs are 1000 feet long, 
171 feet high and span almost a city block, or 237 feet. A large 
air craft factory near Chicago is almost entirely of wood. The 
wooden roof trusses give 150-foot clear span for the assembly 
very 
