262 OHIO STATE ACADEMY OF SCIENCE. 
there is coupled with the small surface exposed a prostrate habit 
which shelters them from the wind and allows them any ad- 
vantage to be gained from warmth radiated from the ground. 
In great contrast to these dwarf creeping almost herbaceous 
forms are the tree willows so well known to every one. These, 
by their rapid growth are enabled to succeed well in their 
favorite habitat along streams and lakes because they can 
quickly repair the damage done by floods and storms, while 
more slowly growing trees would be almost hopelessly beaten 
down and destroyed before they could rear their trunks to a 
sufficient size to enable them to withstand the elements. Like- 
wise their well known ability to grow from cuttings and broken 
branches renders them able to use the very storms which break 
them in pieces as the means of their further dispersal. 
Their well known variability under different conditions is 
an evidence of plasticity of constitution and adaptability to 
various environments which is as important a factor in the success 
of a plant in meeting the competition to which it is subjected as 
is the same quality in the success of aman. From their adapta- 
bility, variability and the large number of intermediates between 
very divergent forms we may safely infer that we have here a 
group of species with a very large amount of “‘ Vital Motion” in 
rapid course of evolution. 
ON USING THE KEYS. 
To construct a key which will hold for all individual willows 
is well nigh impossible, because in the first place, there is a greater 
or less number of hybrids for which no pretense at a key is made; 
and secondly, there is so much variation in some of the species 
that even after including them in two or three different places, 
the writer is not so sanguine as to suppose that he has covered 
all the variant forms. Bearing this probable defect of the key 
in mind, it will be understood that the greater the diligence with 
which each clue given is followed out, the greater will be the 
probability of a correct determination. If the plant you have 
seems to fit in both divisions of the key by all means run it 
through both and after doing so refer to the descriptions and 
plates as well. 
The synoptic table is intended primarily to give some idea 
of the relationships of the different species and consequently the 
whole anatomy of the plant is used while all the parts are never 
present in a single specimen. But in the keys proper every- 
thing is subordinated to the end in view, namely the identifica- 
tion of the plant; and only such characters are used as are actually 
present on a single specimen. In the foot-notes under the keys 
their especial uses and limitations are discussed. 
