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JOURNAL OF THE ROYAL HORTICULTORAL SOCIETY. 



tlie flowering season, and again soon after the formation of the yoiing 

 plums, is advised; the affected flowers or fruit brought down by the 

 shaking to be immediately destroyed. Eemoval of infested twigs and 

 hand-picking of cocoons, &c., is also recommended, besides applica- 

 tions of petroleum emulsion, Bordeaux mixture with tobacco water 

 added, and lime-sulphur-salt wash. 



Experiments are also being carried out in America in another 

 direction. By virtue of a natural law (of equilibrium or parasitism), 

 when a noxious species finds conditions specially suitable to its develop- 

 ment (intensive cultivation being most apt to supply such conditions), 

 it multiphes rapidly itself and furnishes abundant nourishment to its 

 own natural parasites. Those in their turn multiply until they become 

 numerous enough to check the increase of their hosts, when for lack 

 of nourishment they partially disappear and their disappearance permits 

 renewed increase of the noxious species. In America they are trying 

 to make practical use of this law by the cultivation of the parasites of 

 various insect pests, and they have already made great steps in this 

 direction since the law was first formulated by a Frenchman (Perris), 

 in 1866.— M. L. H. 



Polystachya dendrobiiflora, Eeichb. f. By Fr. Kranzlin {Not. 

 Konig. Bot. Berlin, No. 47, vol. v. Nov. 1910, pp. 173, 174).— -The 

 author gives a full description of this orchid from a specimen which 

 had been collected at Dar-es-Salam (in German East Africa) by Mr. 

 Boxberger. The specimen was grown on in the botanical gardens at 

 Dahlem, where it flowered. The only previous description of this 

 species is the rather meagre one of Eeichenbach. — R. B. 



Pometia pinnata (Forst.), Leaves with Unlimited Growth in a 

 Bud Variation of . By W. Magnus (Ann. Jard. Bot. Buit. 3rd supp. 

 2nd pt. 1910, pp. 807-813; 1 plate). — Witches' brooms occur upon 

 trees of Pometia yinnata growing in the gardens at Buitenzorg and 

 elsewhere. They are not due to the attack of any parasitic organism, 

 but are instances of bud variation. The leaflets of the compound 

 pinnate leaves are normally only slightly waved in outline and with 

 serrated margins. The abnormal leaves are more or less deeply cleft, 

 in typical cases right to the mid rib, and the leaf blades are very 

 greatly reduced. The whole leaflet becomes dissected into a number 

 of filamentous parts, which reminds one of the water-leaves of some 

 aquatic plants. The primary segments into which the leaflet is thus 

 divided may become further subdivided and branched. The segments 

 continue to grow for a long time, so tha^/ the leaflet with all its seg- 

 ments may attain a very large size. In this manner large bushes of 

 witch's broom may be formed from the continued growth and branching 

 of only a few leaflets. 



I.seaves of other plants possessing continuous growth are mentioned 

 in the paper {e.g. Welwitschia mirahilis, certain ferns, Guarea Swartii), 

 and it is pointed out that Pometia is unique among them in the 

 character of its growth. — R. B. 



