TOXICITY OF HEAVY METALS 



77 



the tube between one previously formed and the spore itself; in the latter 

 case possibly by new growth from the spore. In many cases a light colored 

 area quite like that considered by Hasselbring to be a pore, could be dis- 

 tinguished, and this may have been present in all cases. Spores which had 

 germinated in drop cultures by forming appressoria were transferred to 

 new cultures in distilled water and returned to the thermostat. Nearly 

 all the appressoria had germinated with normal germ tubes at the end of 

 twenty-four hours. 



An occasional spore germinated normally in a concentration of 0.00005111 

 Pb(NO 3 ),, and a few normal tubes were found in the 0.00004111 concen- 

 tration, but it was only in the o.oooo2m concentration that no effect of the 

 Pb(XO 3 ) 2 upon the germination of the spores was noticeable. In the 

 latter concentration the spores germinated with long tubes, just as in simul- 

 taneous controls in distilled water. 



Series including combinations of Pb- 

 (NO 3 ) 2 with Ca(NO 3 ) 2 were carried out 

 at three different concentrations of the lead 

 salt, o.oooi6m, .0.00033111, and o.ooo66m. 

 With a o.ooo66m concentration of Pb- 

 (NO 3 ) 2 no concentration of the calcium salt 

 was found which entirely suppressed the 

 formation of appressoria and in which only 

 normal germination was produced, though 

 with a concentration of 0.05111 Ca(NO 3 ) 2 

 only a few appressoria were found. This 

 combination gave practically the same re- 

 sults as were found with a 0.00004111 con- 

 centration of Pb(NO 3 ) 2 alone; i.e., some- 

 what over 50 per cent, of the germination was normal, though a considerable 

 number of swellings and appressoria were formed. In the combination of 

 the same concentration of Pb(NO 3 ) 2 (o.ooo66m) with o.oo4m of the cal- 

 cium salt the effect produced was similar to that found in cultures with 

 0.00005111 concentration of Pb(NO 3 ) 2 ; only occasional normal tubes were 

 found, these probably constituting less than I per cent, of the total germina- 

 tion. With concentrations of o.ooim, 0.002111 and 0.003111 Ca(NO 3 ) 2 , com- 

 bined with a o.ooo66m concentration of the lead salt, practically no normal 

 tubes were produced, germination resulting in appressoria and swellings. 

 These concentrations correspond to solutions of Pb(NO 3 ) 2 alone varying 

 in concentration from o.ooim to o.oooim. 



In the second series of combinations of Pb(NO 3 ) 2 with Ca(NO 3 ) 2 , the 

 concentration of the first salt was o.ooo33m and the same concentrations of 

 Ca(NO 3 ) 2 were employed as in the series just described. The results in 



Fig. 4. Spores after four day 

 in o.oo4m Pb(NO 3 ) 2 , X650. 



