242 Transactions of the Royal Canadian Institute 



increased by reflectors. No evidence that a retarding effect of light on 

 growth was obtained. 



3. Other experiments show that humidity is a controlling factor of 

 the highest importance. Within the limits available under the experi- 

 mental conditions, the temperatures were not limiting if humidity was 

 sufficiently high. 



4. Growth rates could also be increased by the removal of leaves or 

 reduced by the removal of conducting tissues. 



5. Although other factors than changing water content, leading to 

 net increase in the solids of the growing tissues (increase in cell walls 

 chiefly) are especially effective in the afternoon, the vacuolar water 

 remains the bulk-maintaining and expanding material, since changes 

 in the environment which affects the water loss from the surface of, or 

 its supply to, the growing part also affect the growth rates during the 

 afternoon as well as during the morning. 



6. The minute amounts of vacuolar emulsoids, namely those aside 

 from the protoplasm and cell-walls, preclude attributing to them any 

 gross contributory effect in growth or shrinkage. Alterations in the 

 protoplasm as an emulsoid complex affecting its permeability, and 

 therefore its behaviour as an osmotic mechanism ; or in the collophysical 

 properties of the cell-walls and their relation to extension under osmotic 

 pressure, with concomitant permanent accretions, are probably to be 

 recognized as' factors to be reckoned with in growth. With regard to 

 the relative importance of imbibition by emulsoids as a growth mechan- 

 ism as compared with osmotic pressure, Opuntia and Eriogonum bear 

 a similar relation to each other as certain pollen grains {e.g., Phaseolus) 

 on the one hand and the embryo-sac (Lloyd, '166) on the other. 



The effect of such conditions, if they obtain in Eriogonum, are masked 

 by the greater effects of the osmotic mechanism as such. 

 McGill University. 



Protocol to Accompany figure 7. 



s, sun; hf, high fog; max. temperature Fahr. in italics; df, dense high 

 fog; f/, red light screen ; 6/, blue light screen ; wz;, li viol glass screen. 



July 21, s; 22, s; 22), hf; 24, 5 71; 25, hf\ 5 after 14 hr. 77; 26, s, hf aiter 

 14 hr. 71; 27, 5 75; 28, s; 29, s, hf after 13 hr.; 30, hf; 31, s. 



August 2,5; 3, df 63 ; 4, dfSS ; 5, df, s after 13 hr. 66; 22, hf 9 hr. 59; 

 12 hr. 75; 13 hr. 80; 18 hr. 59; 23, s, hf (or 15 min. at 10.46 hr.; 9 hr. ys; 

 12 hr. 77; 13 hr. ^7; 18 hr.5p; 24, 5, A/ after 14 hr.; wf 11.35, 104; 25,/?/; 

 8.30 hr. 5p; 12.30 hr. 77; 15 hr. 66; 18 hr. 5<5; 26, s 90; rl 9-11 hrs.; 

 27,hf;bl II hr.onSS; 2S, df; 2g, df; uv 8-i4hrs. 8y, 30, s; hf 10.45; ^ 13-25; 

 hf 13-55; rl till 14 hr. 90; 2,1, s; uv. 



