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.) a7td Corn 

 in Contact with Twined 



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 



(a) Normal 137 



Contact wire 164 19% 



(b) Normal 132 



Contact stakes and twine . 178 34% 



8 Plants in pairs. 24 plants in (a), 36 in (6). 

 ^ Plants in triplets. 



