250 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



decapitated by the removal of the growing-point the leaves change their 

 position, rising or becoming more upright, so as to make a greater 

 angle with the horizon. In some experiments this angle of the petiole 

 •or leaf increased by as much as 40° to 50°, but usually by about 

 10° or 20°. Only younger leaves or those near the growing-point are 

 affected; when an axillary bud develops, as often happens, the reaction 

 ceases. 



The petioles show this movement on decapitation of the stem even 

 when the leaf blade is cut off. The reaction is not affected by light 

 and only influenced, not caused, by gravity. Injury to the growing- 

 point (such as vertical or horizontal incisions) or the enclosure of it in 

 gypsum does not produce the same effect as decapitation. 



The author considers that the reaction is not caused by " Wund- 

 schok, " nutrition, gravity, or light, but that it is due to some unknown 

 stimulus.— G. F. S.-E. 



Leaves and Light {Bot. Gaz. vol. xlviii. December 1909, 

 pp. 459-461; with 1 fig.). — Mr. Joseph Y. Bergen finds (as pointed 

 out by Wiesner) that the upper leaf-surface is in many plants concave 

 for those exposed to sunlight, and not nearly so much so in those that 

 are in shade. The sun leaves of a begonia, e.g. were at an angle of 

 from 23° to 56°, whilst the shade-leaves were at 108° to 180°. Other 

 measurements are also given. — G. F, S.-E. 



Leg'islation to Protect ag-ainst the Introduction of Insect 

 and Fung-US Pests into Victoria {Jour. Dep. Agr. Vict., Septem- 

 ber 1909, pp. 593-602).—" The Victorian Potato Industry: The Inter- 

 State Conference and the Irish Blight," by T. Cherry, Director of 

 Agriculture. An original account of " The Potato Murrain," with illus- 

 trations taken from the " Illustrated London News " of August 29, 

 1846, is given. The importance of the export trade, conditions favour- 

 able to disease, the steps to be taken, and resolutions of the Conference 

 are fully discussed. When once a disease is established, its eradication 

 becomes a matter of great difficulty. The soil may become infected; 

 the remains of one season's crop may carry on the infection to the 

 next year; the micro-organism may betake itself to allied plants, and it 

 may be transferred from one district to another by all kinds of unsus- 

 pected ways. Knowledge of the life-history of the exciting cause may 

 place us on the track of the right means to prevent it, but the con- 

 ditions of life of both the disease and the plant it attacks are so com- 

 plicated that caution has to be exercised in drawing conclusions from 

 any set of experiments. A farmer very often talks as if slight 

 differences in the soil of one part of his farm, or a few weeks' extra 

 dry weather, were solely responsible for this or that result. As a 

 matter of fact, no kind of experimental work is so uncertain as that 

 which deals with plants and animals. The difference existing between 

 living and dead things is so profound that insignificant variations in 

 any respect may make unexpectedly great differences in the final result. 



