408 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Plum, A Study of Sterility in the. By J. M. Barsey (Genetics, vol. iv. pp. 

 417-488, September 1919; 5 plates). — Self-sterility tests show that varieties 

 of the American species are self-sterile. Pollen abortion is not a cause of sterility 

 except in rare instances where suppression is complete. Developing fruits were 

 found to drop in three waves, which are separate and distinct in point of time 

 and size. The first drop takes place immediately after bloom, and is caused 

 by aborted pistils. The second from two to four weeks after bloom and includes 

 all in which fertilization has not taken place. The third, or " June drop," follows 

 the second by an interval of about three weeks, and in these fertilization has 

 taken place, but embryonic development has stopped. 



The suppression of one of the two ovules in each ovary was found to be 

 typical. 



Pollen development and the genetic relationship of varieties and species 

 are also dealt with in some detail. — A. N. R. 



Plum, The Fruitfulness of the, in relation to the weather. By M. T. Dorsey 

 (Jour. Agr. Res. xvii. No. 3, June 1919, pp. 103-126, 3 plates). — Unfavourable 

 weather at blooming time may prevent completely the setting of the fruit of 

 the plum. Rain and low temperatures are also important factors, while strong 

 winds if prolonged prevent pollination by insects at critical times. Wind pollina- 

 tion is not sufficient, even under the most favourable conditions. The chief 

 effects of low temperatures is to retard the growth of the pollen tube. The 

 stigma is receptive for four to six days, and therefore a delay in pollination is 

 liable to render fertilization uncertain. An analysis of the prevailing weather 

 at blossom time shows that, each season, certain conditions can be singled out as 

 being largely responsible for the setting (or otherwise) of the fruit. Remedial 

 measures can be most effectively sought in suitable pollinizers which show the 

 fastest pollen-tube growth. — A. B. 



Pollination of the Mango, The. By Wilson Popenhoe (U.S.A. Dep. Agr., 

 Bull. 542, Aug. 1917; 4 plates, 1 fig.). — Some of the choice introduced varieties 

 of mango fruit very sparingly, except in occasional seasons. The difficulty 

 appears to be due, not to any morphological defect in the pollen, or faulty 

 mechanism of pollination, but to a physiological cause connected with nutri- 

 tional conditions as influenced by changes in soil moisture and food supplies. — 

 A. P. 



Pop Corn. By H. Wenholz (Agr. Gaz. N.S.W. vol. xxix. pp. 534-542 ; 8 figs.). 

 — The large quantities of Pop Corn imported from the United States by New South 

 Wales could with profit be raised in the maize-growing districts of Australia. 

 Pop Corn (Zea Mays everta) is smaller in growth and bears smaller cobs and 

 grain than other kinds of maize. * White Rice' and ' White Pearl' are the best 

 varieties for market. Six or seven grains are sown in clumps placed 3 feet 

 apart. When the plants are about 10 inches high, the weaker growths are 

 removed, leaving three or four vigorous plants in each clump. The corn must 

 be fully matured before it is harvested. — S. E. W. 



Potash in Soil-forming Minerals, The Availability of. By J. K. Plummer 



(Jour. Agr. Res. xiv. No. 8, August 1918, pp. 297-315). — The chief points brought 

 out in this investigation are as follows : 



Little difference in the solubility of potash in water is found among the 

 common soil-forming minerals : Biotite, muscovite, orthoclase, and microcline. 



Biotite and muscovite give up considerably more of their potash to solutions 

 of carbonic acid than do orthoclase or microcline. 



Lime as calcium bicarbonate does not increase the solubility of potash in 

 any of these minerals. Pot experiments with oats, soya beans, rye, and cowpea 

 show that these plants can extract varying amounts of potash from these minerals. 

 Biotite is able to produce four times the amount of dry matter of oats as compared 

 with microcline, and 66 per cent, as much as potassium sulphate. Muscovite 

 produces nearly twice as much dry matter as orthoclase. 



Lime as precipitated carbonate has not materially increased the dry matter 

 or the potash removed from the soil by oats or rye. The dry matter in soya 

 beans has been increased 33 per cent, when lime is used with biotite. Lime 

 causes soya beans to remove more potash from the soil with potassium 

 sulphate, biotite, and muscovite treatments, but does not appear to increase 

 the solubility of the soil potash in N/5 nitric acid in any of the experiments. — 

 A.B. 



