148 SCIENCE PROGRESS 



the free nitrogen of the air and utilising it as food material, 

 has suggested to others that possibly other green hosts with 

 their accompanying parasites might possess similar powers. 

 Perennial shrubs and trees with their mycorhiza suggested 

 themselves for investigations. 



In such an inquiry several conditions suggest themselves 

 as desirable. The host should quickly respond to the presence 

 or absence of nitrogenous food, and should harbour the parasite 

 without, for the most part, suffering any disturbances in its 

 normal mode of life. There should also be a tolerable degree 

 of certainty that the host has been actually invaded by the 

 parasite. These conditions are admirably met by artificially 

 smut-infected cereals. Brefeld cultivated during several 

 successive years several kinds of millet, also barley and wheat, 

 using in some cases infected seedlings, in others infected 

 grains. All the plants were annuals, and reached maturity 

 in the one season. In one series, A, the plants were grown 

 in pure sterilised sand soaked with mineral food solution, no 

 nitrogenous compounds being present. In the other series, 

 B, such compounds were given. After three or four weeks 

 the seedlings in series A ceased to grow, and would have died 

 had not nitrogenous food material in the form of calcium nitrate 

 been added. In series B the plants grew normally and com- 

 pared favourably with the plants from healthy grains grown 

 in the open, until the flowering time, when all the heads in B 

 showed themselves smutty. Brefeld's experiments show that 

 probably ordinary fungi have no power of utilising for their 

 hosts the free nitrogen of the air as the bacteroids {Rhizobice) 

 do for their leguminose ones. 



Summary 



i. Smut and rust are diseases due to fungi, the spores of 

 which were examined and caused to sprout by the brothers 

 Tulasne. Their well-illustrated investigations of sixty years 

 ago hold good to-day, and their hypothesis of close affinities 

 between the two groups has been accepted as an established 

 fact. 



2. Kuhn's observation of the infectibility of oat seedlings 

 holds good, but does not bear the general (and at the same 

 time restricted) application to all corn seedlings botanists were 

 inclined to give it. 



