STONE: CONTACT STIMULATION 463 
were grown close together (about 8 inches apart) and the two series 
of normal plants which consisted of twelve or six in each set were in 
contact with one another throughout their period of development. 
Hence, the percentage gain in growth in height is due to the additional 
contact of the plants to the various materials which surrounded them. 
The largest increase in growth is shown in Table 5 but this data was 
obtained only by the use of 12 plants and probably is exceptional. 
When closely grown plants are surrounded with wire netting, etc., and 
especially large-leafed plants such as the common sunflower the 
leaves do not have an opportunity to assume their normal shape and 
in this way there occurs a tendency to shade the stems. The dis- 
placement of the leaves by the wires thus shading the plants or the 
slight shadow cast by the wire enclosures apparently has little effect 
on the growth in length of the internodes, inasmuch as the same 
reactions can be obtained by growing the plants in darkness. The 
data concerning the results given in the tables (2-9) follow. 
TABLE 6 
Showing Growth of Castor Bean (Ricinus communis L.) and Corn 
in Contact with Twine® 
Average Dimension, etc., in Centimeters 
Experiments No. of Plants Height Faterupdee Percentage Gain in 
J elg j - as 
Used Masabes | ane Height by Contact 
Goa Normals... 2......: 24 81.7 t46. £58 
Contact twine.... 93-6 130 sO: 12%. 0 2F 
Corn (Zea Mays L.) 
a | | 
(Dye Normalln., 5 <0. fi: 36 [226 10.0 12.4 
Contact twine... . | 145.6 10.1 14.0 9% 
TABLE 7 
Showing Growth of Sunflower (Helianthus annuus L.). (a) Average of Twelve Plants 
in Contact with Wire Netting, (b) Average of Twelve Plants in Contact with 
Stakes (Dowels) and Twine’ 
Percentage Gain 
Average Height in Height by 
Experiments (Centimeters) Contact 
(Gy NGENTAE 2 os ci ieg oir cas 137 
Contactewites 42728 35.- 164 19% 
(>) BNocma lcs bye se. faa 132 
Contact stakes and twine.178 34% 
6 Plants in pairs. 24 plants in (a), 36 in (0). 
7 Plants in triplets. 
