32 



death finally occurs, results in a renewal of g-rowth bv means of 

 new lateral shoots and roots. This type of dying has not been 

 observed in broad bean plants g-rown in pot culture, and it is 

 concluded that suflicient boron is present, as a trace has been 

 detected in the soils used. 



2. — The absence of boron does not cause death in barley, 

 gfrowth being healthy in ordinary culture solution. 



3. — Excess of boric acid is poisonous to the broad bean, injury 

 being apparent with one part of boric acid (H3BO3) in 5,000 parts 

 of the water culture medium and with 0.5 gm. or 1.0 gm. per 

 22| lbs. of soil in pot culture, according to the method of 

 application. 



4. — Boric acid is more poisonous to barley than to the broad 

 bean ; in water culture a concentration of one part of H3BO5 in 

 2,500,000 parts of nutrient solution, and in pot culture .5 gm. per 

 22|^ lbs. of soil is injurious. Smaller quantities are either in- 

 effective or slightly favourable, though the benefit is usually 

 evident to the eye only and not shown in the dry weight. 



5. — Injury is marked by (i.) retardation of germination, (ii.) 

 first chlorosis and later brown markings of the leaves ; the barley 

 leaf becomes spotted but that of the broad bean shows a band of 

 brown along the margins. (iii.) Retardation in maturing in the 

 case of barley in soil culture. 



6. — Preliminary experiments show that several other plants, 

 and especially Pliaseohis multiflorus and Trifolium incarnatum, 

 appear to benefit from the addition of small quantities of boric 

 acid to the nutrient solution, though rye, like barley, is apparently 

 indifferent to low concentrations. 



7. — Boron is found to be present in considerable quantity in 

 the dried shoots of the broad bean plants grown in a nutrient 

 solution containing no boron, and also in the seed. In garden- 

 grown plants a larger proportion of boron was present in the pods 

 than in either the stems or leaves. No more than a trace was 

 jdetected in the barley seed or in the dried shoots of untreated 

 barley grown in water culture. 



8. — It is suggested that the function of boron in the case of 

 the broad bean is probably nutritive rather than catalytic, since a 

 supply is required throughout the life of the plant. A parallel is 

 drawn between the action of boron on plants and the \ itamines on 

 animal life. 



VI. Kathekine Wakin(;ton. "TJie hijhiencc of Manuring 

 on the Weed Flora of Arable Land/' journal of 

 Ecology, 1924. Vol. XII. 



Examinations have been made of the weed species j^resent on 

 the variously manured plots of fields which ha\e been cropped 

 continuously for a considerable period with : — 



1. Winter wheat (Broadbalk Field). 



2. Spring barley (Hof)s Field). 

 .3. Mangolds (Barn Field). 



The data show that the chief factors which determine the dominant 

 species are the crop and the methods of cultivation, the most 

 important weeds being quite different in the three fields. Winter 

 fallowing has a particularly striking influence on the weed flora. 



