January io, 191 8] 



NATURE 



Z^2> 



ficially heated were used for the cultivation of 

 tender plants. Since then, however, the evolution 

 of the greenhouse has been rapid. There are now 

 glass structures, acres in extent, so cleverly made 

 that the cultivation of plants in them is as suc- 

 cessful as in the open with the most favourable 

 Aveather conditions. The market gardeners of 

 England have in the last fifty years made great 

 progress in the art of glasshouse gardening, and 

 in the United States, where the sun affords in 

 winter more heat and light than it does here, 

 huge structures are erected for the forcing of 

 flowers and vegetables. 



Mr. Wright, director of the New York State 

 School of Agriculture and formerly a professor of 

 horticulture, has collected in his book a large 

 amount of helpful information concerning the loca- 

 tion, adaptation, erection, and equipment of 

 greenhouses to suit American weather conditions 

 and requirements, which both builders and gar- 

 deners will be certain to appreciate. 



The conditions in England are somewhat dif- 

 ferent; still, a great deal of Mr. Wright's teaching 

 may be applied in the making of houses, frames, 

 etc., in this country, and in methods of heating 

 them. Our old greenhouses are too heavy and 

 obstruct the light too much. A good plant-house 

 must be strong, yet light, and it must cast very 

 little shade. The angle of the roof, quality of 

 glass, methods of ventilation, and the internal 

 arrangements with respect to benches and floors 

 are all questions of great importance, as Mr. 

 Wright clearly shows in his well-illustrated 

 chapters. 



(2) V^etable forcing as- practised In the United 

 States is the subject of an excellent treatise by Mr. 

 Watts, Dean and Director of the School of Agri- 

 culture and Experiment Station at Pennsylvania 

 State College. Forcing as practised in horticulture 

 is the application of artificial heat to the growth 

 of plants out of season. It is now very largely re- 

 sorted to for the production of food vegetables in 

 winter, enormous quantities of fresh, wholesome 

 vegetables being grown in this and other coun- 

 tries where, without it, they would be difficult to 

 obtain. It is also largely practised for the pro- 

 duction of certain flowers, especially roses, carna- 

 tions, daffodils, and violets. Where sunshine in 

 f winter is fairly constant successful forcing is easy, 

 as, for instance, in the United States, where there 

 is far more winter sunshine than in England. In 

 greenhouses and frames specially constructed for 

 the purpose perfect crops are produced in mid- 

 winter of such vegetables as cabbage, cauliflower, 

 lettuce, radish, tomato, cucumber, rhubarb, 

 asparagus, French bean, and mushroom. A know- 

 ledge of the treatment of soils, suitable manures, 

 right temperatures and ventilation is necessary, 

 and is best obtained by actual experience. Useful 

 guidance can also be obtained from books, such as 

 that by Mr. Watts, which sets forth the best 

 methods of the American practitioners. They believe 

 in soil sterilisation by means of steam or formalin. It 

 is found that the soil continues to be productive year 

 after year when it is annually sterilised, whereas 

 NO. 2515, VOL. 100] 



without this it becomes "sick " and infested with 

 fungi and other causes of disease in plants. 

 Stable manure is preferred to all other fertilisers, 

 but nitrate of soda is sometimes used as a growth 

 stimulator. ^ Greenhouse construction, heating, 

 insect enemies and diseases, and marketing are 

 carefully treated. The statement that plants 

 are rendered susceptible to disease by high tem- 

 peratures, excess of water, and over-manuring will 

 be endorsed by practical cultivators in this 

 country. 



(3) The propagation of fruit trees by means 

 of grafting, budding, layering, and cuttings is 

 essentially the same in all countries. The methods 

 vary, as does the skill with which the operations 

 are performed. In America, where fruit-growing 

 is done on a very large scale, labour-saving 

 methods are practised. Orchards miles In area 

 have to be planted and worked, for which men 

 with spades and pruning-knives would be as 

 Inadequate as they would be for agriculture. The 

 alert Americans have therefore sought the assist- 

 ance of the machine-maker for their digging and 

 planting operations, and even for binding in the 

 operation of grafting. 



Prof. Brown's book enables us to realise what a 

 big industry fruit-growing has become In America. 

 There are nurserymen there who each dispose of 

 young trees by the million annually. "The 

 growing of all the twenty to forty millions of 

 American-grown apple seedlings that are used In 

 this country every year is undertaken by less than 

 a dozen firms." In addition, large quantities of 

 young trees, both stocks and "maidens," are 

 imported from Europe. At this rate America will 

 soon be covered with fruit trees unless they are 

 used up quickly, as roses are In that country. 

 Some of our own fruit authorities advocate 

 this Intensive system on the ground that young 

 trees properly managed give their best in the first 

 few years, after which they should be scrapped. 

 Apples, pears, plums, cherries, peaches, and a few 

 other fruits are invariably grafted or budded on 

 stocks known to influence growth and frultfulness. 

 Too little care, however, is exercised in the selec- 

 tion of stocks. Prof. Brown discusses the Influence 

 of scion on stock In regard to commercial fruit 

 trees. His book is written for students, a number 

 of what he calls "review questions " being set out 

 at the end of each chapter, such as "What Is 

 meant by Influence of stock over scion?" It 

 contains numerous helpful illustrations. 



W. W. 



ANALYTICAL DYNAMICS. 

 A Treatise on the Analytical Dynamics of Par- 

 ticles and Rigid Bodies: with an introduction to 

 the Problem of Three Bodies. Bv Prof. E. T. 

 Whittaker. Second edition. Pp. xIi + 432. 

 (Cambridge: At the University Press, 1917.) 

 Price 155. net. 



THE first edition of this book was reviewed In 

 Nature of April 27, 1905. At that time 

 what we now call aeroplanes only existed In 



