23 



ometer apparatus — the gift of Robert Mond, Esq. — is now being 

 set up, and the sources of error eliminated preparatory to a general 

 investigation of the nature of soil acidity. 



Many farms in tlie country are short of lime, but agricultural 

 advisers are often in the difficulty that they cannot tell a farmer 

 exactly how much lime the soil needs : often, indeed, they can only 

 say that he should apply between 10 cwts. and 2 tons per acre. Of 

 course, if farming were independent of cost, this vagueness would 

 not matter, but the delicate financial balance under which agricul- 

 ture has to be conducted leaves no margin for indecision between 

 10 cwts. and 2 tons. It is hoped that one result of these investiga- 

 tions will be to enable experts to give more definite advice than is 

 now possible. 



During the period under review, two voluntary workers have 

 assisted in the work of the department — Mr. V. A. Tamhane, 

 Soil Physicist to the Bombay Presidency, and Mr. H. Raczkowski, 

 of the Palestine Experimental Station. 



SPECIAL ENTOMOLOGICAL INVESTIGATIONS. 



In addition to the important investigations on the insect and 

 other invertebrate fauna of the soil already dealt with on p. 20, the 

 Entomological Laboratory has undertaken the following work : — 



(1) A study of the biological phenomena of Aphides. The 

 results are set out on p. 49. 



(2) Chemotropisw. Dr. A. D. Imms, in conjunction with 

 Mr. H. M. Morris, has extended his previous work (p. 48) on the 

 responses of insects to chemical stimuli. This property opens up 

 the possibility of controlling certain injurious insects which cannot 

 satisfactorily be dealt with by insecticides. The method of experi- 

 ment is to expose uniform amounts of various chemical substances 

 in a series of traps for a constant length of time and to identify the 

 species and the sex of the insects that respond. 



(3) Wireworm investigations have been carried out by Mr. 

 A. VV. Rymer Roberts on the biological side, and in conjunction 

 with Mr. Tattersfield on the chemical side (p. 43) . 



(4) In view of the urgent necessity for systematising the sub- 

 ject. Dr. A. D. Imms is preparing an advanced text book of en- 

 tomology for the use of research students, which it is hoped to 

 complete during the present year. A beginning has also been 

 made towards the formation of insect collections which will be 

 essential for purposes of identification and research. 



(5) Insecticides. By common consent the subject of insecti- 

 cides is not well advanced, and efforts will be made to obtain much 

 needed fundamental knowledge. On the chemical side, 

 Messrs. Tattersfield and Roach have investigated Tuba root 

 {Derris elliptica) from which they have extracted two crystalline 

 substances, some resins, an oil and an amorphous substance, 

 apparently a saponin. Of these the resins and one crystalline sub- 

 stance are toxic. Methods have been devised for comparing the 

 toxicities of these products, and also of different consignments of 

 the root. In addition a chemical method for evaluating the root 

 has been elaborated. 



