Vol. XII. No. 295. 



THE AGRICULTURAL NEWS 



281 



The jjrai]iial extinction whuh these factors biiDg 

 about causes national scientific loss as regards living 

 records and possibilities of ncolngjcal studies: whilst 

 there is no less a depreciation in the country's natural 

 beauty. In so far as the exterminating forces can be 

 arrested without detriment to noi mal economic devel- 

 opment, action should be taken to iloso. 



But the subject has another side. Wild plants 

 act as hosts to certain parasites of cultivated plants. 

 Wild plants, also, — particularly mesophytes and hydro- 

 phytes — occupy useful land. Also there is the spread 

 of weeds to be considei-ed. In the West Indies exam- 

 ples of these points are afforded in the cases of root 

 diseases of permanent crops, froghopper attacks on the 

 sugar-cane, forest land in islands awaiting further devel- 

 opment, and the spread of weeds like the Mexican 

 poppy, and parasites like dodder and mistletoe. 



Regarded broadly, the subject is interesting and 

 instructive, and is well worth corsideration in the 

 West Indies. Here inconsiderate extension of cultiv- 

 ated areas is harmful in regard to forest land and 

 water-supply, and in the direction of spoiling natural 

 features of interest which tend to attract visitors. 

 The primeval forest in the Virgin Islands is a case to 

 be borne in mind in both these connexions. Some 

 restraint might be exercised in many places as regards 

 the unnecessary erection of buildings in areas of 

 scientific or even of merely artistic interest. 



The Watering of Plants. 



Some suggestive considerations in regard to the 

 above subject appear in the form of a leading article 

 in the Gardeners Chronicle for ■)u\y 12, 191-^. 



The amount of water which any particular plant 

 re(|uires depends partly upon its composition, but 

 chierty upon its biological characteristics. In regard to 

 the roots of plants, it has to be borne in mind that 

 a saturated soil is as fatal to health as a dry one. In 

 applying water it has also to be remembered that 

 a relation exists between the amount of water necessary 

 and the state of the plant. It is possible, for example, 

 to prevent plants from flowering by supplying them 

 continuously with plenty of water. Even more inter- 

 esting is the circumstance that both light watering 

 and heavy watering produce no difference as regj.rds 

 increase in yield. This fact has been proved by inves- 

 tigations at the French Natural School of Horticul- 

 ture. At first sight, it might seem a matter of indiffer- 

 ence as to what time of the day watering is done. 

 The chief scientific explanation of the well-established 

 prejudice against watering in the sun is that the 

 addition of water to a hot soil disengages a considerable 

 quantity of heat — particularly in clay soils containing 

 a large proportion of organic matter. This may often 

 bring about serious damage to th'- roots. When plants 

 are grown under glass, and, to some extent, under 

 shade, it is possible to control water requirements by 

 regulating the amount of moisture in the atmosphere. 

 In the case of glass-houses, this can be done by spraying 

 the leaves. Incidentally, it may be noted that this ques- 

 tion of humidity is a factor of considerable importance 

 in cacao cultivation. 



Referring again to the que.stion of the effect of 

 watering upon the temperature of the soil, observations 

 made in the West Indies seem to point in the opposite 

 direction to those already noted. In considering the 

 subject of watering of plants in general, it is always well 

 to bear in mind the difference between this way of 

 applying moisture and its normal receipt in the form 

 of rain. A characteristic feature which distinguishes 

 the addition of water to the soil is that, in the artificial 

 supply, a great deal is wasted by surface How, by evap- 

 oration, and by horizontal diffusion in the soil. 



The World's Production and Consumption of 

 Mineral Manures. 



The International Institute of Agriculture has 

 recently issued a comprehensive statistical account 

 of the above subject, under the title of Pro- 

 duction et Consommation des Engrais Chimiques 

 dans le Monde. The chief feature of general interest 

 is the maps showing by means of numbered and 

 coloured circular areas the relative consumption and 

 output in different countries. It is interesting to note, 

 in regard to production, that the chief mineral phos- 

 phate-producing regions, are in Older, the south-eastern 

 United States, Tunis, France, Algeria, Hungary, the 

 South Sea islands, the West Indies (Rodonda) and' 

 Russia. Nitrate of soda, of course, comes entirely 

 from Chile. Sulphate of ammonia is produced chieHy 

 in Germany, England and France. Guano, as is well 

 known, comes from the islands off the coast of 

 Peru. Perhaps the most striking fact is the enor- 

 mous output of potash manures from Germany. Not! 

 only is this output greater than that of an}' other 

 mineral manure, but it is restricted entirely to 

 Germany. Crude saltpetre, however, which contains 

 potash as well as nitrogen, comes from India. 

 Synthetic manures — nitrate of lime, calcium cyanamide 

 etc. — are manufactured in Norway and Sweden, Italy, 

 Austria, the United States and Canada. 



The most intensive consumption per acre of mineral 

 manures goes on in Belgium and Holland. These 

 countries are followed by a group, composed of Germany, 

 England, France, Australia, the south- e.-istern United 

 States, and Italy; then come the north-eastern United 

 States Austria, Spain, Algeria and Tunis, Borneo, Japan, 

 Scandinavia, and Ireland. The next degree of 

 decrease in intensity characterizes that remaining parb 

 of the North American continent not referred to above. 

 In Argentina, Chile, Russia, India and Arabia the 

 intensity of consumption is still lower than in Canada. 



Unfortunately the consumption throughout the 

 tropical zone has not been determined, with the 

 exception of that for northern Australia, India, Borneo 

 and Mauritius. 



Figures showing the importations into the Westj 

 Indian islands are given however; for instance, Trinidad 

 and Tobago imported during 1911 mineral manures 

 valued at 65:-!, 495 francs; whilst for Barbados the figure* 

 for the same year are given as :i, (5(35,037 francs. The 

 figures for the past ten years, in the case of eacJx 

 Colony, exhibit great variation, 



