37 



October in each year. The production of the sexual forms goes 

 on until the following May. If, however, a temperature above 

 70° F. is maintained, asexual reproduction only occurs, suggesting 

 that the change from the asexual to the sexual method of repro- 

 duction is directly influenced by temperature. 



The gout fly investigation made by Mr. Frew arose out of 

 a field problem. It was found that couch grass is the chief winter 

 host, and that certain manures, especially farmyard manure and 

 superphosphate, enable the barley plant to escape damage by 

 inducing early growth of the ear out from its ensheathing leaves. 

 Once the plant is infestated, however, nothing can be done : pre- 

 ventive measures only are possible, and of these, early sowing 

 and suitable manuring are the most important. 



In the Mycological Department, the chief work has been 

 the study of wart disease in potatoes by Dr. Brierley, Miss 

 Glynne and Mr. Roach, and the commencement of an investiga- 

 tion into mosaic disease of plants by Dr. Henderson Smith. 

 Reference has already been made to the discovery that a dressing 

 of finely powdered sulphur at the rate of 12 cwts. per acre 

 intimately mixed with the soil greatly reduces, and probably 

 eliminates, the disease from light soils. Another practical 

 application of the work results from Miss Glynne's discovering 

 how to infect susceptible varieties with the disease. At present 

 the only method of testing the immunity of new varieties is to 

 grow them for a year or more on badly infected soil. By using 

 Miss Glynne's method described on p. 66 it is possible to dis- 

 criminate between susceptibles and immunes in a few weeks, a 

 matter of great importance to the plant breeder. 



The work on mosaic disease started with the discovery by 

 Dr. Bewley of the Cheshunt Experimental Station of nodules 

 containing certain organisms which appeared on tomato-extract 

 culture-media inoculated with juice of plants suffering from this 

 disease. The work already done indicates that similar nodules 

 may arise on these media when inoculated with other organisms 

 not connected with mosaic disease ; but that they also occur 

 readily (perhaps more readily) after inoculation with certain 

 organisms obtained from mosaic-diseased plants. Dr. Henderson 

 Smith is in touch with the members of the Committee on Foot 

 and Mouth disease, there being points of similarity in the two 

 enquiries. 



It has already been stated (p. 32) that algae apparently play 

 a part in the highly important nitrogen cycle of the soil; the 

 study of these organisms is carried out in the Mycological Depart- 

 ment by Dr. Bristol Roach. The work has necessitated the isola- 

 tion in pure cultures of a number of species of algae from tHe soil 

 and the growth of these organisms on artificial media in order to 

 discover some of their physiological properties. Dr. Bristol Roach 

 has been able to show that most algae grow better in presence 

 of small quantities of certain soluble carbon compounds than 

 when they are completely dependent on carbon dioxide in sun- 

 light for their source of carbon ; the exact order of preference 

 for these substances varies with the particular species. 



