156 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Recommendations as to treatment of affected trees were : 



1 . That all diseased trees be heavily pruned early in winter, and all affected 

 shoots and branches be burned forthwith. 



2. That leaves from such trees should be collected as soon as possible after 

 falling and burned. As the spread of the disease is most probable through the 

 agency of affected leaves, this recommendation is most important. 



3. That the trees, after being pruned, should be sprayed with Bordeaux 

 mixture during winter, and again when growth begins in spring. 



4. That it is essential for the control of this and other diseases of trees that 

 adequate spraying machinery should be provided for the purpose. 



5. That all nursery trees be carefully inspected prior to planting. — C. H. H. 



Pleione Pricei Rolfe (Bot. Mag. t. 8729 ; October 1917). — Native of Formosa. 

 A plant which thrives well in the tropical house, with flowers lilac or rosy lilac 

 with a whitish lip, which is blotched with pale brown and ornamented with 

 yellow keels. — L. C. E. 



Pollinia of Orchids. By R. A. Rolfe (Orch. Rev. xxvi. pp. 194-198). — A 

 review of the structure of the pollinia of orchids from the simple pollen grains 

 of the ancestral Apostasiae to the highly complex arrangement in the higher 

 groups where the grains are not only aggregated into pollinia, but further united 

 to a portion of the rostellum, known as the stipes and gland, which all come 

 away together when an insect visits the flower. The rostellum is a modified 

 stigma, yet it is retained in the male flowers of Catasetum, showing the anomaly 

 of a female organ first losing its proper function and assuming another, and 

 becoming an adjunct to the male pollinary apparatus ; finally, on the sexes 

 qecoming separated, remaining as an essential part of the organization of the 

 male flower. It is given as a beautiful illustration of the working of Natural 

 Selection through a long series of beneficial modifications. — R. A. R. 



Polygonum Griffithii Hook. By C. H. Wright (Bot. Mag. t. 8724 ; August 

 191 7). — Native of Northern India and Western China. A good perennial for 

 the rock garden, quite hardy, but fails to mature seed. P. Griffithii closely 

 resembles P. sphaerostachyum, but its flower spikes are smaller and on longer 

 peduncles. Flowers deep crimson with buff-coloured bracts which form an 

 effective contrast. — L. C. E. 



Potato Leaf-roll : its Ciagrosis and Cause. By E. J. Wortley (Phytopathology, 

 viii. pp. 507-529, Oct. 191 8 ; figs.). — Leaf-roll is prevalent in potatos in Bermuda 

 as well as in many other districts. The author reports sixty varieties to have 

 been seen attacked. Several other troubles have been confused with this, but 

 he regards as a most important diagnostic character the rolling of one or more 

 of the lower leaves. The rolling may be only the slight upturning of the leaf 

 margins or may be cylindrical. The affected leaf is yellowish, especially the 

 apical portion of the terminal leaflet, and the texture is hard and crisp, the 

 affected leaves remaining rigid during drought. The whole plant is smaller, 

 yellower especially during dry weather, has shorter stolons, and gives a much 

 smaller yield than normal plants. The disease is transmissible by planting tubers 

 from affected plants. He regards the disease as being the product of climatic 

 conditions, especially drought, and gives a number of observations and experi- 

 ments in support of his claim. He considers that soil-infection plays no part 

 in the propagation of the disease, but does not appear altogether to reject 

 Quanjcr's hypothesis (see Jour. R.H.S. xlii. p. 505) of the disease having 

 origin in the attack of a specific organism, for he reports that certain experiments 

 carried out on Prince Edward Island prove that the progeny of healthy parents 

 that have grown near diseased plants develop leaf-roll. — F. J. C. 



Potato Diseases, Resistance to. By G. H. Pethybridge (Jour. Dep. Agr. 

 Ireland, xviii. Dec. 191 8). — The varieties Great Scot, Provost, Kerr's Pink, 

 Dominion, and Burnhouse Beauty, resistant to wart disease, proved susceptible to 

 ordinary blight, pink rot, and canker (Spongospora subterranea). — F. J. C. 



Potato Seed Experiments. By T. C. Johnson and J. T. Rosa (U.S.A. 

 Exp. Stn., Norfolk, Virginia, Bull. 24). — The largest potato crop was obtained 

 from i-8 oz. tubers planted whole. Cut seed potatos sprout more quickly 

 than whole potatos. For early crops, ' Irish Cobbler ' gave the best results. 



S. E. W. 



Potato Spraying. By G. H. Pethybridge (Jour. Dep. Agr. Ireland, xviii., 

 Dec. iqi8). — Comparisons of the results of spraying with 1 per cent, and 2 per cent, 

 solutions of Burgundy mixture on different varieties of potato are given. The 

 results were sometimes in favour of the higher, sometimes of the lower strength, 

 Frequent sprayings were much more effective than single ones, — F. /. C. 



