106 Explanation of Plates. 



Fk;. 5. — Antirrhinum seedlings after treatment. The control (U.V. ) 

 curved up. The lowest vaselined plant turned up at first and 

 then curved downwards. 



Fiu. 6. — Ivy-leaved Pelargonium after treatment. In the control (U.V.) 

 the stem and young leaves curved up. In one of the vaselined 

 plants (V^^) both young leaves and the stem curved downwards. 



Fig. 7. — Two stems of the same species showing downward curves after 

 treatment. 



Fkj. 8.— Stem apex of the plant in figure 6 (V."). Experiments by Miss 

 M. W. Rea. 



PLATE II. 



Fig. 9. — Seedling of Cerastium niter treatment. The control (U.V.) was 

 an older plant. Ilie lower two vaselined plants show downward 

 curves. Photographed in tlie erect position in order to show the 

 targiditj' of the curves. 



Fia. 10. — A similar plant after treatment. Photographed erect. 



FniS. 11-14. — Reversal of gravity-curvature in sunflower seedlings placed 

 in 13 to 16 per cent, carbon dioxide and recovery of normal cur- 

 vature. Experiments by Miss M. J. Lynn. 



Fig. 11. — Reversed curvature of six seedling stems in carbon dioxide, 



Fio. 12. — Recovered normal curvature in the same seedlings after the 

 carbon dioxide had been removed. 



Fig. 13. — Reversed curvature in eight out of nine seedling stems in carbon 

 dioxide. 



Fig. 14. — Recov^ered normal curvature in the same seedlings after removal 

 from the jar into fresh air. 



PLATE III. 



Fig. 15. — One plant of Anthemis sp. with one branch vaselined and show- 

 ing reversed curvature, the other unvaselined showing normal 

 curvature and elongation. Experiment by Miss M. W. Rea. 



Figs. 16-20. — Reversal of gravity curves and light curves in carbon dioxide, 

 and recovery of both normal curvatures. Experiment by Miss 

 I. Finnegan. 



P'iG. 16. -^Sunflower seedlings in carbon dioxide growing aioay from light 

 and dovn wards. 



Fig. 17. — The same plants after removal to fresh air, showing recovery of 

 normal response to gravity in one seedling. 



Fk;. 18. — The same a day later, showing recovery of normal gravity- 

 curvature in both seedlings. 



Fir. 19. — The same a few more days later, showing recovery of normal 

 light-curvature in both seedlings. 



Fig. 20. — The same still later, a to b reversed heliotropism ; h to c re- 

 versed geotropism ; c to d recovered normal geotropism ; rf to e 

 recovered normal heliotropism. In one seedling the recovered 

 light-curve is in the new growth [d to e) ; in the other it is in the 

 older part of the stem [d^ to e'). 



