166 MISSOURI BOTANICAL GARDEN BULLETIN 
A few measurements on Norway maples and sweet gums 
gave similar results: 
COMPARATIVE GROWTH OF NORWAY MAPLES AND SWEET 
GUMS FOR 1919-1922 
| Norway Maples Sweet Gums 
Tree No. | 1 2 3 4 1 2 
hist 3 2 2 4 2 2 
Ce 1 1 1 1 a 1 
| Sr 4 3 3 3 4 3 
DOOE cx cas sea. 2 4 4 2 8 4 
Since climate was the only factor which could have had a 
similar influence on all of these trees we may conclude that 
1919 and 1920 were goed growing seasons and that 1921 and 
1922 were much less favorable. Inasmuch as silver maples 
make most of their growth during a relatively short period in 
the spring, we have here an index to the weather of that season 
during the last four years. If we knew more about the re- 
quirements of the different species of trees we would be able, 
by studying their twigs, to determine the weather most favor- 
able for growth over a long period of years. 
PLANTS OF VERY LIMITED LOCAL DISTRIBUTION 
The following plants, most of which have a wide general 
distribution, are confined to very limited areas within our 
local territory. For this reason they are particularly inter- 
esting to the student of local plants and are deserving of 
propagation and protection. 
TREES AND SHRUBS 
Acer rubrum var. tridens. 
A variety of the red maple represented by a few trees near 
Allenton. This variety can be distinguished from the species by the 
leaves, which are small, obovate, narrowed or rounded, and subentire 
or sparingly toothed below the three short lobes, the middle lobe 
being broadly triangular. General distribution: Mass. to Fla., 
Mo., and Tex. 
Ascyrum hypericoides, St. Andrew’s cross. 
This is the smallest of our native shrubs, its maximum height not 
exceeding eight inches. It is found scattered on the sand hills near 
Allenton and Pacific. Distribution: Mass. to S. Ill., Nebr., and 
southward. 
