Effect of Boron Compounds 73 



of contact diminishes, but solutions of the same concentration do not act 

 equally on all seeds. Boric acid and borax proved to be similar in their 

 action qualitatively. 



The deleterious effect of strong doses of boric acid on germination 

 was confirmed by Agulhon (1910 a), the higher quantities (above 10 mg. 

 boric acid per litre) retarding germination of wheat. 



3. Does boron stimulate higher plants ? 



Of recent years a few investigators have thrown out hiuts as to the 

 stimulant action exerted by boron compounds on plants. Koxas indi- 

 cated that M/100,000 (M = molecular weight) of boric acid exercised 

 a favourable action on rice. Nakamura (1903) tested the point by 

 means of pot cultures. Peas and spinach plants were grown in soil 

 which received 1 and 5 mg. borax per kgm. With peas the 1 mg. exerted 

 evident stimulant action, as determined by the increase in height of the 

 shoot over that of the control, 5 mg. seeming to be slightly depressant in 

 action. With spinach a stimulation was observed both in weight and 

 height with a dose of 5 mg. borax per kgm. 



Average weight Average length of leaves 

 " 5 mg. borax 10-35 38-2 



Control 7-2 34-0 



Agulhon (1910 c and d) took the matter up still more definitely and 

 made many tests of various kinds, in water, sand and pot cultures. 



(a) Water cultures. 



His water cultures were made under sterile conditions, the seeds 

 when possible being sterilised with corrosive sublimate, the germinating 

 apparatus being also sterilised. With wheat a stimulant action was 

 evident, maximum growth being obtained with between 2o and 10 mg. 

 boric acid per litre, though the dry weight increase did not quite keep 

 peice with that of the fresh weight, a fact to which previous reference 

 has been made. The chief improvement is in the root, the stem/root 

 ratio falling to 5, as against 6 in the control series. Visual observation 

 indicated that the roots of plants receiving 5 — 10 mg. boric acid per 

 litre are longer than the others, though they are less rich in adventitious 

 roots. The increased dry weight due to boron may amount to as much 

 as 30%. 

 (6) Sand cultures. 



Agulhon again observed stimulation in this case. 2 kgm. of sand 

 were moistened with 500 c.c. nutritive solution, varying quantities 



