32 \ SCIENCE PROGRESS 



the Conidia, and in the terminal growth. The septa are 

 sparse and irregular in their distributicm, whilst owing to the 

 narrowness of the hyphse (o'5-r2 /i) little is known as to 

 the cytology. Metachromatic granules are present in the vege- 

 tative parts, and in the spores there are present granules of 

 uniform size and with the staining properties of nuclei. 



Actinomycetes occur abundantly in many soils, particularly 

 those rich in undecomposed organic matter, in consequence 

 of which they tend to attain a maximum frequency in the 

 autumn. Of the 25 soils from different localities studied by 

 Waksman and Curtis the average number per gram of soil 

 was 870,500 as compared with 4,245,000 bacteria. Like the 

 latter, there is a decrease with increasing depth, but in rela- 

 tion to the bacteria a proportional increase. Waksman (191 9) 

 in an extensive paper deals with the features and behaviour 

 of a number of species on culture media. This author finds 

 that for most species the minimum temperature is below 18- 

 20°, and the maximum above 40°. Whilst they will not grow 

 under strictly anaerobic conditions, several are semi-anaerobic. 

 Most are actively proteolytic, producing ammonia and amino- 

 acids as a result of their metabolism. Starch affords one of 

 the best sources of carbon, though most species can also 

 assimilate dextrose, maltose, lactose, mannite, glycerine and 

 inulin. All liquefy gelatin and nearly all reduce nitrates. A 

 few species are capable of utilising cellulose. The paper is 

 accompanied by a key for the identification of species by 

 means of their biochemical reactions. 



Genetics, etc. — According to Dorsey {Genetics, September 

 1 9 1 9), the American varieties of Plum are self-sterile, but though 

 aborted grains were found in all cases, this is seldom complete 

 or the cause of sterility. There are three successive periods at 

 which the pistils are shed, viz. {a) immediately after flower- 

 ing, {b) two to four weeks after blooming when fertilisation 

 has not occurred, (c) four to six weeks after blooming when 

 fertilisation has been effected but the embryo development 

 has been checked. The cause of sterility is attributed to the 

 slow growth of the pollen tubes conditioned by genetic con- 

 stitution. 



A race of Fagopyrum tataricum has been studied by Zinn 

 {Genetics, November) in which the number of carpels varied from 

 3 to 25 with 4 carpels as the mode. The perigones also exhibit 

 a varying number of segments (5-18) with 5 as the mode, and 

 there was positive correlation between the number of seg- 

 ments and the number of carpels. Selection, whether of 

 normal or abnormal seeds, appeared to have no effect on the 

 type of variability. High temperature and humidity favoured 

 the development of abnormal flowers, which also were most 



