156 ILLINOIS ACADEMY OF SCIENCE 
18. Artemesia caudata Michx. Tall or Wild Wormwood. 
Dwarf plants numerous—one plant measured 12 mm. or a 
little less than half inch over all and bore 1 persisting cotyle- 
don, 5 leaves and 1 flower. Another perfect plant measured 
18 mm. over all. The writer is most familiar with this species 
in dry sandy places where it grows to be a tall weed. Britton 
& Brown give the size as 2°-6° high, and Robinson & Fernald 
gives it as 0.5-1.5 m. high. 
In addition to these dwarf species there are a few plants 
of the wild bean (Strophostyles helveolus) which had evidently 
germinated in late summer and bore a blossom or two, They 
were, however, far from mature. 
Now, one striking feature of this dwarf flora was that 
while the dwarfs varied considerably among themselves as to 
size, the whole flora was markedly dwarfed, not merely single 
individuals here and there. This fact, along with the fact that 
several unrelated species were involved, indicated that some 
markedly dwarfing influence was at work. 
In seeking an explanation, two obvious facts forced them- 
selves upon the attention: one was the persistence of the cotyle- 
dons on many of the plants, indicating that they were not only 
dwarfed, but young precocious plants, and another was that 
the ground where they grew was considerably below the high- 
water line of the river, which covered the ground where they 
grew until considerable late in the season. They would there- 
fore have a considerably shorter growing séason than their 
upland relatives. Although, as will be stated more fully here- 
after, this shortness of season is in itself hardly sufficient to 
explain adequately the dwarfness of the plants, it is one factor 
which we can give in terms of more or less precise measurement 
by a consultation of records of the weather and of the river 
stages. They are therefore given in considerable detail, es- 
pecially as, on account of their measurableness, they can be 
represented in compact, graphic form. 
The strip along which the dwarf plants were found growing 
was between about 6.21 and 6.50 feet above the low water 
mark. Now, during the early part of the season—from May 
9th to May 22d, on June Sth to 8th and from June 14th to 
July 28th, the water was above the 6.50 stage. Even with 
