296 EXPERIMENTAL STATIONS — REPORT FOR 1879. 



next year's report, accompanied probably with the results of a 

 second crop, for it is gratifying to know that it is the intention 

 of the Marquis of Tweeddale to continue the experiments. 



EXPERIMENTS ON THE GROWTH OF BARLEY GROWN IN POTS UNDER 

 GLASS, BEING A DUPLICATE OF THE HIGHLAND AND AGRICUL- 

 TURAL society's field EXPERIMENTS. 



"When everything has been done that care and attention can 

 secure and experience suggest in the conduct of field experiments, 

 there still remain many disturbing influences beyond the control 

 of the experimenter, which, if they do not defeat his aims, at 

 least greatly retard his progress. These are mainly the in- 

 fluences of weather and season, and it was to eliminate these, 

 and so form a check upon the results obtained at the Society's 

 stations, that the experiments here described were undertaken. 

 Tlie soil used was a very poor one, and it was worked together 

 with the spade, and twice riddled before it was put into the pots. 

 Tlie pots were bags made of stout canvass, about 10 inches in 

 diameter, and 15 inches deep, and the same weight of soil was 

 put into each. The object in using canvas bags was to overcome 

 some serious obstacles wdiich ordinary clay pots present to the 

 attainment of accurate results in the carrying out of comparative 

 manurial experiments. It is well known to gardeners that com- 

 mon garden pots differ greatly in thickness, porosity, and com- 

 position, and that these differences afiect the growth of the plants 

 they contain. The more porous kinds of clay permit of greater 

 eeration of the roots, more rapid drainage and evaporation at the 

 external surface, and consecpiently require more frequent water- 

 ing. The temperature of the earth in them is also affected by 

 the porosity of the pot, the more rapid evaporation determining 

 an amelioration of temperature. The substance of the clay itself 

 is not imaffected by the roots of plants, and some kinds and 

 textures of clay are more easily acted on than others. 



In experiments where the effect of a few grains of manure is 

 to be noted, such differences as these may be very disturbing ; 

 but the most serious objection is one which is common to all 

 clay pots, and is most conspicuous in the best of them. It is a 

 matter of common observation that the outside of these pots 

 becomes covered over with a white incrastation. This consists, 

 for the most part, of salts which have been dissolved out of the 

 earth and the clay of the pot, and which have been left behind 

 wdien the water which held them in solution was evaporated at the 

 surface. It is noticed chiefly on parts of the pots exposed to free 

 air or the sun's rays, and, as the salts forming it are part of the 

 food of plants, they are by this process carried out of reach of 

 the rootlets. The extent to which this goes on depends, among 



