324 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the soil, the leaves turn yellow and drop, or become reddish brown 

 and die without falling. Later the cambium dries, and with the phloem 

 and cortex turns brown and disintegrates. The roots are the first to 

 suffer, then the base of the tree. Various fungi and boring beetles 

 speedily take up their abode in the dead tissues and hasten destruction. 

 Characteristic odours are developed in trees destroyed by gas, and 

 various chemical substances may be discovered in the dead tissues, 

 which owe their origin to the gas absorbed. Illuminating gas does 

 very great damage to foliage, different plants showing different degrees 

 of damage from this source ; but, as with most plant-poisons, under 

 certain conditions it acts as an accelerator of plant-growth, and the 

 author describes some experiments illustrating this phase of its action. 



F. J. C. 



Geotropic Stimulation, Chemical and Physical Changes in. 



By Eva O. Schley (Bot. Gaz. Dec. 1913, pp. 480-489 ; with 6 figs.). 

 — In a growing shoot, the acidity is greatest at the tip, decreasing 

 downwards. When a shoot is geo tropically stimulated, the concave 

 side becomes at first relatively more acid. The acidity, however, 

 afterwards decreases until the maximum is on the convex side. 



When there is visible curvature, the two plants show equal acidity 

 and remain so until the tip has passed the vertical plane, when the 

 concave side again becomes acid. These changes are not parallel 

 to the relative rates of growth of the two sides. The percentage of 

 dry weight is greatest on the concave side. — G. F, S. E. 



Geotropy of Flax. By Josef Pohl {Beih. Bot. Cent. xxxi. Abt. i. 

 Heft 3, pp. 394-409; with 21 figures). — The author describes the curious 

 changes in flax during growth. During the juvenile period the stem 

 shows distinct negative geotropy, which is displayed by the young 

 stem itself and in the hypocotyl, beginning to act in the latter organ 

 under the cotyledons and gradually affecting the lower part. Next 

 follows the first period of nutation (due to thermotropy), during 

 which the tip of the stem is bent over downwards. If the tip is cut 

 off, it straightens itself, becoming upright, in about two hours. This 

 period occupies 9-1 1 days. Next an inflorescence axis is produced, 

 and, during this phase, transversal geotropism is more developed. 

 Direct sunlight can now no longer induce the stem to straighten itself. 

 But during this second phase the stem becomes upright at night. The 

 next stage is that of flowering ; each peduncle becomes vertically 

 upright when the flower is polhnated, and the inflorescence-axis also 

 becomes shghtly more erect and nearly vertical as soon as the first 

 two flowers are in fruit. The transversal geotropism of the flowering 

 stage changes to marked negative geotropy in fruit. The advantage 

 of this change hes partly in th^ better support of and partly in the 

 better opportunity of distributing the fruit. Direct sunhght, however, 

 overcomes transversal geotropy and the flower peduncle becomes 

 more erect. — G. F. S. E. 



