THE SOIL AND ITS EFFECT ON PLANT GROWTH. I9 



ing dissolved nutritive salts. By the time ear formation begins, 

 the formation of " white roots " ceases, and those already formed 

 become branched and eventually approximate more closely to the 

 normal type of root. It thus appears that the formation of "white 

 roots" takes place in order to meet the needs of the plant at a time 

 when a sudden increase in food is essential for the production of 

 tillers. As efficient tillering is an important factor in relation 

 to the yield of a crop, the need of further study of the conditions 

 which promote the growth of " white roots," and their possible 

 encouragement by appropriate manuring, is obvious. The in- 

 vestigation is therefore being continued with wheat plants, and 

 will be extended to other cereals and cultivated grasses. 



In the Botanical Department also, research has been going on 

 for some years to find out whether plant poisons applied in very 

 small quantities act as a stimulant to plant growth. The most 

 important results so far obtained have been with boron. Broad 

 bean plants grown in water cultures and in pots respond by a very 

 definite increase in growth, amounting to about 10 per cent., to the 

 addition of very small doses of boric acid, whereas a heavy dose 

 will kill the plants. It is proposed to carry out field trials 

 with barley and broad beans to ascertain whether the addition 

 of small quantities of boron to the ordinary manures, would be 

 advantageous and practicable. 



Much attention has also been given during the last twelve years 

 to the subject of farm weeds, particularly in their relation to 

 types of soil. The results obtained up to 1919 were incorporated 

 in a book entitled " Weeds of Farm Land," which was published 

 in 1920. Since then special attention has been paid to the collec- 

 tion of information regarding the weeds growing on various types 

 of soils. An attempt is being made to secure from all parts of the 

 country, through the medium of pubhc schools, training colleges, 

 and possibly elementary schools, information regarding the weeds 

 growing in all districts, the soils on which they grow, their relative 

 frequency, &c. These particulars are being tabulated so as to 

 secure, for every important weed, information regarding its dis- 

 tribution and habitat, particularly with reference to the type of 

 soil on which it grows and the crop with which it is associated. It 

 has already been established that very few individual weeds can 

 be regarded as indicators of definite soil types, but it seems likely 

 that groups of weeds will afford a fairly safe index to the nature 

 of certain soils. Information is at the same time being secured 

 as regards local measures of eradicating and preventing weeds, 

 so that such knowledge may be spread over a wider area. 



