TOXICITY OF HEAVY METALS 63 



of the medium along the streak. The acervuli are visiWe in from two to 

 five days after inoculation. 



Before the spores were used in the experiments, the stock cultures were 

 allowed to grow undisturbed from ten to fifteen days, a procedure which 

 insured a sufficient quantity of spores fro.n a single tube for the inocula- 

 tion of an entire series of experimental cultures. Preliminary tests indi- 

 cated that spores from acervuli in the same tube, but of different ages', 

 were not at all uniform in viability. Direct inoculation of the culture 

 dishes from the spore masses of the stock tubes was thus shown to be 

 unsatisfactory, since it was not only desirable that all cultures contain 

 approximately the same number of spores, but also that the percentage of 

 viability of the spores in all cultures should be as nearly alike as possible. 

 It also seemed desirable to avoid small pieces of agar and bits of mycelium 

 in the liquid cultures, for such contamination might influence the effect 

 of the salts in the solutions on the germination of the spores, as by 

 absorption or the formation of new chemical compounds. The plan was 

 therefore evolved of allowing the stock cultures to grow for from ten to 

 fifteen days, after which period the spore masses were carefully removed, 

 with a platinum needle, to a clean area on the agar surface, from which, 

 after thorough mixing in a little heap, the inoculations to the water cul- 

 tures were made. This method usually resulted in satisfactory uniformity 

 in the germination of the spores in the various controls, from which 

 fact it was concluded that all cultures thus made contained an approxi- 

 mately equal number of viable spores, and that any inhibition or modifi- 

 cation of germination must be due- to properties of the culture medium 

 rather than to differences in the spores introduced. 



In comparing the effect of the various media upon the spores, the main 

 criterion was the presence or absence of germination after a period of 

 eighteen hours. In many cases, however, germination was more or less 

 modified, as in the production of swollen tubes and other abnormalities, 

 and such modifications of germinal activity needed frequently to be taken 

 into account. As has been indicated, it was seldom necessary to consider 

 the percentage of normal germination which occurred, but in many cases 

 the proportion of abnormal to normal growth was approximately 

 determined. 



These Gloeosporiurh spores possess several very favorable features for 

 such an investigation as the present. They are readily wetted by water 

 and aqueous solutions and, being slightly heavier than water, they sink 

 quickly to the bottom of a hanging drop. They germinate readily in dis- 

 tilled water in from three to four hours and produce long filaments in 

 eighteen hours, a feature which is of considerable advantage here, for it 

 is quite conceivable that the influence of various chemical compounds on 



