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 Irom 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 irom 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'. 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. 

 l°/„ 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 



' "II apparott done que lea graines foarnieB par des plantes ayaut era en prfiaenoe 

 d'une quantity de bore filev^e pr^aentent une acooutumanoe via-A-vis de oet ^lAment • les 

 planta auxquela ellea donnent naiaaance sembleut non aeulement faire un meilleur emploi 

 dea petites doaea de bore qui leur sent offertea, maia encore aupportent les doses toxiques 

 pluB faoilement que lea planta ttooina, iasus de graines non aoooutumies." 



