72 Effect of Boron Compounds 



are peas and oats, for with these one-half the original amount of boron 

 (= 1 gm. per sq. metre) proved toxic. 



Interesting results were obtained (Agulhon 1910 a) by repeated 

 experiments with the same soil containing boron. It was found that 

 sand or soil containing a proportion of boron which is lethal or toxic 

 to a first culture will allow much better growth with a second and 

 subsequent crops. Repeated experiments on the same soil may show 

 the change from a lethal dose to a toxic one, thence to an indifferent 

 and finally to an optimum concentration. Furthermore (Agulhon 

 1910 b) the very plants may accustom themselves to greater quantities 

 of boron, the increased power of resistance being transmitted. He 

 concluded from his experiments that the progeny of the second gene- 

 ration of maize were able to withstand quantities of boron that were 

 toxic to control plants 1 . Agulhon once again emphasised the fact that 

 for toxic doses of boron the first symptom is the more or less marked 

 disappearance of chlorophyll, though the aerial parts are not affected 

 so soon as the roots. 



2. Effect of boron compounds on germination. 



One of the first indications that boron compounds affect the germi- 

 nation of seeds was given by Heckel (1875) who found that germination 

 was retarded for 1 3 days by weak solutions of borates ( - 25 gm. to 

 20 gm. water), and was stopped altogether by stronger solutions ('60 gm. 

 to 20 gm. water). Archangeli (1885) tested the germination of a variety 

 of seeds of Leguminosae, Gramineae, and of Cannabis, Iberis, Rapha- 

 nus, Collinsia, and Linum in the presence of boric acid. The seeds were 

 placed in bowls with solutions of "25, '5, and 1 / boric acid at tempera- 

 tures ranging from 16 23 C. The bowls were covered with glass 

 plates to prevent evaporation and consequent increase of concentration, 

 controls in spring water being dealt with under similar conditions. 

 1 / boric acid was found to check germination altogether, and the 

 weaker the concentration the less was the process hindered. Morel 

 soaked seeds of haricots and wheat in various solutions of boric acid, 

 and found that germination was generally hindered or inhibited. The 

 deleterious action diminishes as the strength of the solution or the time 



1 " II apparait done que les graines fournies par des plantes ayaut cru en presence 

 d'une quautit^ de bore eleve'e pre'sentent une accoutumance vis-a-vis de cet element ; les 

 plants auxquels elles donnent naissance sembleut non seulement faire un meilleur emploi 

 des petites doses de bore qui leur sont offertes, mais encore supportent les doses toxiques 

 plus facilement que les plants te'moins, issus de graines non accoutume'es." 



