uf f/ic T n i- iii ^j (Brassica napus). 



451 



why the sections treated with the watery extract of the alcoholic 

 precipitate exhibited no marked plasmolysis. 



That the oxalic acid formed by P. <.l<'4rndan* in Pasteur's solution 

 acts as a powerful toxin was very clearly shown. Six plugged and 

 sterile test-tubes were prepared, and about 10 c.e. of the fermenting 

 Pasteur solution was poured into each. To three of these (series 1) 

 sufficient calcium carbonate was added to neutralise the oxalic acid. 

 Both series of tubes were then sterilised by discontinuous boiling, 

 during which process the cytase would be destroyed, and into both 

 when cool freshly cut and sterile sections of turnip were placed 

 prepared as described on page 446, and the solutions allowed to act 

 till next morning. The sections in the second series of test-tubes 

 showed a marked contraction of the protoplasm, and it looked brown 

 and dead, and showed no tendency to return to its normal condition 

 when immersed in pure water. In the first, which were treated with 

 calcium carbonate, the protoplasm was quite normal, and exactly 

 resembled a section which had been immersed in sterile water for the 

 same period. 



A third set of test-tubes were filled with about 10 c.c. of the 

 solution; these were not boiled, and received no calcium carbonate; 

 the sections introduced showed complete dissociation of the cells, the 

 cell-walls greatly swollen and the protoplasm very strongly contracted. 

 This experiment with the Pasteur solution demonstrated the produc- 

 tion of the same cytase, and strikingly illustrated its effect upon the 

 plant cell, as well as the toxic action of the oxalic acid ; even more so 

 than was the case with the same experiment with turnip juice. 



In considering the effect of the oxalic acid upon the cells, it is 

 important to note that calcium pectate, a salt which is decomposed by 

 oxalic acid with the production of calcium oxalate, enters largely into 

 the composition of the middle lamella. Wehmer has shown that in 

 the cultivation of Asperyillus niyer and Pmidllinni ijlmwnn oxalic acid 

 is formed in saccharine solutions, that the oxalic acid produced acts as 

 a toxin to these fungi, and gradually diminishes their vigour, and that 

 when a certain strength has accumulated no further development is 

 possible; growth, however, is resumed when the oxalic acid is neutralised 

 by a calcium salt. The reaction between the oxalic acid produced by 

 P. destrnctans and the calcium pectate of the middle lamella is 

 preciselly analogous : the oxalic acid would be neutralised, and the 

 pectate replaced by the oxalate, and the continued growth of the 

 bacteria would thus be rendered possible. The oxalic acid* then both 

 acts as a toxin in killing the cells aiid may also play some part in 



* Since the above account of the formation of oxalic acid by P. destructan.t was 

 written, Zopf lias published a note also describing the formation of oxalic acid by 

 B. xylinum, " Oralsaurebildung durch Bacterien," ' Berichfce d. D. Bot. Gesell.,' 

 Feb. 1900. 



2 K 2 



