lo June, iqi-^-J 



WcUer Req/{irc///e//is of Crops. 



355 



On comparing the results with those given for other countries on 

 Table I., it will be seen that the ratio is higher than those obtained for 

 cereals in Europe, but lower than American and Indian results. It caniiot 

 be said, however, that the comparison with the Burnley pots is quite 

 satisfactory. In the earlier stages of growth the crops suffered from 

 undue shading, and in the latter stage from the same influence at certain 

 hours of the day. It has already been mentioned that transpiration is most 

 active in bright light, and practically ceases at night. In connexion with 

 this, it would be expected that the transpiration ratio would be higher 

 for plants grown in the open air than in plants partially shaded most of 

 the time. It has recently been shown by Dr. H. Brown that it would 

 be about one-half greater. Accepting this figure instead of the average 

 figure 483, we should then have a transpiration ratio of 725 for oat plants 

 grown in the open. The Indian figure for oats is 870, and it appears 

 likely that 725 more nearly expresses the ratio for the Australian climate 

 than the results given in the table. 



In discussing the question of assimilation it has been pointed out that 

 the transpiration ratio is chiefly dependent upon the climate, but that it is 

 not altogether so. In this connexion an important practical point was 

 recently established by Dr. J. W. Leaiher of the Agricultural Research 

 Institute, Pusa. In the dry climate of India the transpiration ratio tends 

 to be high. It was found, however, that crops grown with manures made a 

 better use of the water than crops with no manure, as is seen by the 

 decreased ratios in every case. 



Table III. 



The first four are cold weather crops, in which evaporation is rapid, 

 the last a monsoon crop, during which season the atmosphere is humid and 

 moist giving generally low ratios. In discussing the results the author 

 points out that not only does superphosphate have effect in narrowing 

 the ratio, but that nitrates also, if required for plant food, and as might 

 not be anticipated, have a like effect. After an elaborate series of experi- 

 ments lasting some years, it is stated that " the effect of a suitable manure 

 in aiding the plant to economize water is the most important factor which 

 has yet been noticed in relation to transpiration." 



In concluding consideration of this subject it should be pointed out 

 that the provision of a pot-culture house, on lines similar to those erected 

 in other countries, is essential if the influence of local conditions upon the 

 water relations of plants in Victoria is to be successfully studied. At 

 Burnley a large number of pot cultures failed owing to the want of 

 suitable equipment, and the re.sults from those few which have completed 

 have had to be discussed with reserve. 



The following conclusions have been arrived at : — 



I. In cold humid climates, from 200 to 300 tons of water is lost by 

 transpiration for each ton of dry crop yield. 



