58 SCIENTIFIC REPORTS OF THE AGRICULTURAL RESEARCH 



plants were infected with seed of 0. cernua collected from 

 0. cernua upon tobacco and with seed of 0. indica collected 

 from 0. indica upon mustard, from 0. indica upon tobacco, 

 from 0. indica upon cabbage and from 0. indica upon 

 turnip. The same treatment was applied to mustard 

 and to the other host plants. The results showed that 

 0. cernua was strongly parasitic upon tobacco and did not 

 attack the other three hosts, while 0. indica was not para- 

 sitic upon tobacco unless the seed used had been collected 

 from plants which were parasitic upon this host, in which 

 case such seed was not capable of infecting mustard plants 

 with " tokra.' 1 Seed of 0. indica collected from plants 

 parasitic upon either mustard, cabbage or turnip, however, 

 would not infect tobacco but was strongly parasitic upon 

 all of these hosts. Thus there appear to be two races or 

 strains of 0. indica, one parasitic upon tobacco and not in- 

 fecting mustard and the other parasitic upon mustard, or 

 the allied cabbage and turnip, and not infecting tobacco. 

 Certain of the pot cultures received heavy applications of 

 sodium nitrate, which, however, did not have any marked 

 effect upon the occurrence of the tokras; the details and 

 results of all the above experiments are now in the press. 



(3) Phytophthora investigations. Mr. Dastur has 

 continued his studies on this important genus. The Black 

 Thread disease of Para rubber trees is fully described in the 

 Memoirs and, as a result, the attention of other workers has 

 been directed to the similar condition prevalent in Ceylon 

 and Java. It seems clear that the disease is found in most 

 parts of the East where rubber is grown, but the Java work- 

 ers still hold that it is due to the same parasite that causes 

 the well-known rubber canker, and is not a new disease. 

 Mr. Dastur has given reasons for believing the parasite to 

 be a distinct species, a matter of considerable economic im- 

 portance since the canker fungus is common especially in 

 the neighbourhood of infected cacao trees. He has found 

 the Black Thread fungus to be much more restricted in its- 

 parasitism than Phytophthora Faberi, the canker fungus, 

 and has quite failed to get it to attack cacao and other hosts 



