STONE: CONTACT STIMULATION 457 
conducted in a conservatory where the heat, light and soil conditions 
were uniform and normal. Some of the experiments were carried on 
in direct sunlight; others in darkness, while others again were con- 
ducted under bell glasses where it was possible to maintain uniform 
atmospheric moisture and transpiration conditions. Contacts with 
wire were made with a two-inch-mesh galvanized iron wire netting, 
and in some cases a one-inch-mesh wire was employed. These were 
made up into cylinders 4 to 6 feet high and varied in diameter from 
8 to 26 inches, according to the size and number of plants employed. 
These wire cylinders were placed around the plants. In some in- 
stances the plants were grown between trellises made of wire netting 
placed from 6-10 inches apart, in which case the tips or free end of 
the leaves of the plants came in contact with the wire on two sides. 
Wooden stakes (dowels) and iron posts driven into the soil were also 
employed as contact material, the dowels being used in some instances 
to support loose twine which surrounded the plants and in other 
cases they were used alone in various combinations. Fishnet made 
of twine with a mesh of about two inches was employed in a similar 
manner to that of the wire cylinders, and in some cases the plants were 
more or less loosely tied up with twine. In the study of the effects 
of contact on the stems and roots of seedlings, excelsior was employed 
either loosely in long strands, or cut up more or less in fine shreds as 
the nature of the experiment required. In the root, contact experi- 
ments were made with soil particles which ranged from 16 mm.—o.I mm. 
in size, the various grades of material being obtained by sifting through 
sieves and bolting cloth. The particles were repeatedly washed and 
sterilized and submerged in jars of water, the latter being previously 
boiled to exclude air, inasmuch as the presence of air would greatly 
modify the growth of the seedlings (1). 
EFFECTS OF CONTACT OF PLANTS WITH ONE ANOTHER 
When plants are grown close together, as is the case of some crops, 
they often come in contact with one another and even in nature con- 
tact stimulation plays an important réle, particularly where certain 
organisms grow so close to one another that they touch. The growth 
of some coniferous trees is often such that they are much congested, 
and in nurseries where many thousands of coniferous seedlings and 
other nursery plants are grown close together a contact stimulation 
may sometimes occur. We have, however, no authentic data based 
upon experiments regarding the behavior of coniferous and other 
seedlings grown under nursery conditions. Neither have we attempted 
to differentiate growth which may be due to contact in thick stands 
of forest growth from those originating from other causes, but some 
