68 SCIENTIFIC REPORTS OF THE AGRICULTURAL RESEARCH 



order to establish the scientific basis on which legislation 

 must rest, an examination of the factors controlling the dis- 

 semination of parasitic fungi has been completed and pub- 

 lished. Two types of dissemination should be distin- 

 guished : continuous or short-range, and discontinuous or 

 long-range. For the former, fungi are so well equipped 

 that measures to check it are likely to prove abortive : for 

 the latter, on the other hand, a great body of evidence has 

 been got together to show that, if we exclude human agency r 

 fungi are not in a position to make such considerable jumps 

 as to be able to cross the seas or spread from one part of the 

 world to another at all readily. Most of the important 

 plant diseases that have appeared in recent years can be 

 traced to the movement by human agency of the living plant 

 which they attack, from one part of the world to another; 

 they follow trade routes; and when, one after another, the 

 more isolated parts of the world are brought into contact 

 with western civilization and opened up to trade and ex- 

 ploration, each lets loose its indigenous pests and diseases 

 to infect the countries with which commercial relations 

 become established. It is not realized how thoroughly new 

 countries are searched for economic plants, nor how quickly 

 attempts are made to introduce novelties, or even varieties 

 of already cultivated kinds, from them. It is open to ques- 

 tion whether the benefits gained from such sources are not 

 more than counterbalanced by the new diseases that have 

 thus been introduced. 



The book on fungi causing crop diseases in India, refer- 

 red to in last year's report, has been completed and is now 

 in the press. It deals with the general principles of plant 

 pathology and gives a detailed account, crop by crop, of the 

 more important diseases of cryptogamic origin found in 

 Indian field and plantation crops. 



VI. Systematic Work. 



This has been largely in abeyance during the year, partly 

 owing to the difficulty of obtaining foreign assistance under 

 present' conditions. Several collections have been identified 



