4 i6 APPENDIX 



pressure side, in all cases, even when this is the side in the erect position com- 

 pressed by the wind. The response, hence, does not appear to be due to the 

 stimulatory action of gravity, but Sonntag concludes that heliotropic influences take 

 part in inducing the differentiation. 



Observations by Ewart and Mason- Jones (Annals of Botany, 1906) upon the 

 formation of red wood in lateral and main axes of Cupressus and Pinus bent 

 forcibly into a circular form, show that the red wood mainly appears upon the under- 

 surfaces whether these are stretched or compressed, and thence spreads into the 

 neighbouring vertical or nearly vertical regions of the curved axis. It appears 

 therefore to be the result of a gravitational stimulus, which spreads along the same 

 side from the point directly stimulated. It is difficult to see how differences in 

 the intensities of illumination on the upper- and under-surfaces could act in the 

 way Sonntag supposes upon the living cambium of old stems covered by thick 

 opaque layers of bark. Nor can differences of temperature come into play since 

 otherwise red wood would appear on the sunny side of an erect stem. 



Formative and Inductive Action of Light. According to observations made by 

 Dr. Buller at Birmingham, one half to one hour's exposure to light is sufficient to 

 induce the formation of a pileus upon the branching strands of Polyporus squamosus 

 developed in darkness. After several weeks' continuous darkness, however, small 

 patches of spore-bearing tubes are formed at intervals on the under-surfaces of the 

 strands, but some were even formed upon the upper-surface of an imperfectly 

 developed pileus. In normal healthy pilei, the hymenial tubes are positively geo- 

 tropic in both light and darkness. 



Autonomic Movements. Molisch (Ber. d. D. bot. Ges., Bd. xxn, 1904, p. 372) ob- 

 served very rapid autonomic movements in Oxalis hedysaroides, H. B. K., the leaflets 

 falling suddenly or in jerks through i to i^cm. in 1-12 seconds. 



Photonastic and Thermonastic Movements. W. Wiedersheim (Jahrb. f. wiss. Bot. r 

 1904, Bd. XL, p. 230) finds that the photonastic and thermonastic movements of flowers 

 and leaves involve a general acceleration of the average rate of growth, which is shown 

 even when movement is prevented. This is produced first on the concave side, and 

 later on the convex, which latter results in a more or less pronounced return curva- 

 ture. Since a forced mechanical curvature does not cause any such return curvature 

 when the leaf is released, it can hardly be due to an autonomic orthotropic response, 

 as Schwendener and Jost suppose it to be. In other words, both sides of the leaf or 

 halves of the pulvinus react in the same way, but one responds more rapidly than the 

 other. The fact that Impatiens parviflora performs its sleep-movements on a klino- 

 stat, and hence is ' autonyctitropic/ was first observed by Fischer (Bot. Ztg., Bd. XLVIII, 

 1890, No. 42). 



Dispersal Movements. The spores of Agaricus, Polyporus, Boletus, Coprinus, and 

 other Hymenomycetes, do not merely fall off, but owing to the sudden rupture 

 of the stretched cuticle are jerked off with sufficient energy to clear the hymenium, 

 without striking the opposite gill-lamella or pore-wall. The vertical arrangement 

 allows them to fall clear, but, owing to their small size, they descend in still air, in 

 accordance with Stokes' formula with a constant velocity of from a few mm. to cms. 

 per second. (Observations by Buller at Birmingham.) 



