76 Effect of Boron Compounds 



III. EFFECT OF BORON COMPOUNDS ON CERTAIN OF THE 

 LOWER PLANTS. 



Our knowledge of the action of boron on the lower plants is less 

 definite and complete than with regard to the higher plants. Morel 

 (1892) found that boric acid acts as a strong poison to the lower fungi 

 and similar organisms, their development being completely arrested by 

 very weak solutions of the acid. He suggested, on this account, that 

 boric acid might be used in the same way as copper to attack such 

 diseases as mildew, anthracnose, &c., which attack useful plants. 



On the other hand Loew (1892) stated that such algae as Spirogyra 

 and Vaucheria showed no harmful influence for many weeks when the 

 culture water contained as much as *2/ (=1/500) boric acid. This may 

 be supplemented by a recent observation at Rothamsted, in which 

 certain unicellular green algae (unidentified), were found growing at the 

 bottom of a stoppered bottle containing a stock solution of 1/100 boric 

 acid. 



Agulhon (1910 a) dealt chiefly with yeasts and certain ferments, and 

 found that yeasts grown in culture solutions are not influenced favour- 

 ably or unfavourably by relatively large quantities of boric acid up to 

 1 gram per litre, while all development is checked with 10 grams per 

 litre. The presence of boron affects the action of yeast on glucose and 

 galactose. Galactose alone is not attacked even after 40 days in the 

 presence of "66 / boric acid. When glucose is mixed with the galactose 

 the latter is said to be at first left untouched, but later it disappears 

 very slowly. 



Boric acid exercises an antiseptic action on lactic ferments, 5 gm. per 

 litre checking their action sufficiently to enable milk to remain unco- 

 agulated. Lactic acid is still produced even with as much boric acid as 

 10 gm. per litre. The microbe is not actually killed by the boric acid, 

 but its development is so arrested that reproduction cannot take place. 

 The same phenomenon was observed with yeast. With moulds again, 

 while no stimulation could be obtained with small quantities of boric 

 acid, yet the toxic action does not begin to set in until 5 gms. boric acid 

 per litre are present. 



Thus it appears that such lower organisms as yeast, lactic ferment 

 and Aspergillus niger are remarkably indifferent to the action of boric 

 acid, as is shown by the fact that the toxic dose is remarkably high, 

 while stimulation effects cannot be observed even in the presence of the 

 smallest quantities yet tried. 



