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 (i). 



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 role, 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 



