April 23, 1920] 



SCIENCE 



403 



tween 1828 and 1845, during which period 

 1,373,091 three-ruble pieces were minted, be- 

 sides a few six-ruble and 12-ruble pieces. The 

 three-ruble piece was worth $2.33 and it 

 weighed 10.3 grams, for platinum was then 

 worth but $7 an ounce ; with platinum at $165 

 an ounce, the intrinsic value of such a coin 

 to-day would be more than $54 of our money. 



In view of the fact that the platinum out- 

 put continues to be much smaller than some 

 years ago, while the increasing demand for 

 jewelry purposes offsets the falling off in the 

 demand for munitions processes, it appears 

 likely ihat the price will continue to go up, at 

 least until the full resumption of platinum 

 mining in Russia serves as a check. The 

 search for the discovery of new sources is 

 being diligently prosecuted, and Colombia 

 seems the most hopeful of all the regions ex- 

 cept Russia. 



The newspaper notoriety given to platinum, 

 because of the great legitimate demand for it 

 and the consequent astonishing rise in value, 

 before long excited the cupidity of dishonest 

 persons. As a consequence of this there have 

 been numerous thefts of the material. In sev- 

 eral cases, valuable specimens of platinum 

 have been purloined from museum collections, 

 and chemical utensils made of platinum have 

 been stolen from a number of chemical labora- 

 tories. Indeed, in one instance an entire uni- 

 versity laboratory was burned down to hide 

 the theft of platinum. 



As to future prosi)ects, an extensive devel- 

 opment of the platinum resources in the 

 Republic of Colombia is in active progress. 

 Possibly Canada may contribute somewhat 

 by improved methods of refining the copper- 

 nickel ores, and similar ores mined else- 

 where may also furnish considerable plat- 

 inum. However, the most encouraging sign 

 is the reported determination of Soviet Russia 

 to issue platinum certificates, that is to say, 

 certificates secured by the platinum stock that 

 has been accumulated in Russia and has not 

 fallen into the hands of the Allies, or will be 

 mined now and in the future. 



George F. Kunz 



SEXUALITY IN MUCORS. II 



" NEUTRAL " RACES 



As regards the intensity of sexual reaction, 

 however, a gradation is clearly shown. A 

 more detailed view of the complete table 

 showing the combinations only where reac- 

 tions might be expected, can be seen more 

 clearly (Table I.). The higher grades of A 

 and B predominate at the upper left-hand 

 corner while at the opposite comer are only 

 O's with C's and D's between. There is there- 

 fore in this species, varying degrees of sexual 

 activity from the strongest down through the 

 weakest to so-called " neutrals " which fail to 

 show any sexual reaction under the conditions 

 of the experiment. The word " neutral " is 

 obviously only a relative term since, if the "two 

 races Nos. 811 and 367 had not been used as 

 testers, No. 370 would have been classed as a 

 neutral. It is possible that the 3 so-called 

 neutrals would have taken part in zygospore 

 formation if strong enough testers of the 

 proper sex had been available or if more 

 favorable environmental factors had been 

 present. The fewer the number of tests made 

 and the more imfavorable the environmental 

 conditions, the larger will be the nimaber of 

 races listed as neutral from any collection of 

 races of a given species. 



A change in sexual activity tending toward 

 neutrality may be brought about by environ- 

 mental factors. Thus we have obtained a tem- 

 porarily neutral condition in both the plus and 

 minus races of Mucor Mucedo by growing them 

 for several non-sexual generations at unfavor- 

 ably high temperatures. The sexual activity 

 can be regained in a few generations by culti- 

 vating them at low temperatures. In the same 

 species the spores in a germ sporangium 

 frequently are neutral in reaction but later 

 become sexually active. One of my most active 

 forms (Mucor V) has become much reduced 

 in sexual activity since its opposite races were 

 first separated some sixteen years ago. A 

 similar reduction in sexual vigor resulting in 

 neutrality has been reported in a niimber of 

 species by other investigators. In Phycomycet 

 the plus and minus spores in a germ sporan- 



