1706 DISEASE DUE TO FUNGI. - GENERALITIES 



The results of the soil analyses show that in the case of the oranges 

 there is a marked inverse correlation between the humus content of the 

 soil and the percentage of mottling, the latter tends to diminish as the humus 

 content increases. A statistical study of the data shows that 50 per cent 

 of the cases of mottling can be accounted for by the low humus content 

 of the soil. The humus content of the lemon soils studied averages less 

 than 0.1 per cent, an amount which is too small to produce a normal 

 growth, and which is nearly always associated with mottling. 



No correlation was found between the proportion of mineral carbonates 

 in the soil and mottling ; it was noticed that in lemons the mottling de- 

 creased slightly as the mineral carbonates increased, but the changes were 

 so slight that it cannot really be considered as a case of correlation. In all 

 the soils examined the lime content is low, and its application in large 

 quantities benefits lemon trees more than orange trees, more especially 

 when the soil is rich in humus. 



There is no relation between the total nitrogen and mottle-leaf either 

 in oranges or in lemons. The greater the proportion of organic carbonates 

 with regard to the humus, the more the leaves of the tree are attacked ; 

 and in the same way, the more proportion of humus is raised the more 

 the disease is checked. This does not prove that humus is the organic sub- 

 stance best fitted to give rise to the development of healthy and normal 

 leaves, but it shows that in a soil which is able to convert organic matter 

 into humus, the organic matter, during the process of decomposition, 

 passes through stages when it is very readily absorbed b}^ the plant roots. 

 Addition of organic substances which can readily be assimilated to the 

 soil is therefore suggested as a new means of checking the attacks of mot- 

 tle-leaf. 



DISEASES DUE TO FUNGI, 

 BACTERIA AND OTHER EOWER PEANTS. 



GENER.\LiTiEs 1226 - CHmatic Conditions as related to Cercospora bet/cola. — pool, v. w,, and 



Mc Kay, M. B., in Journal of A agricultural Research, vol. VI, n. i, pp. 21-60, fig. i-io, 

 PI. III-IV. Washington, D. C, 191 6. 



Experimental work on the subject in hand leads to the following 

 conclusion: 



i) The life of the fungus Cercospora bet i cola wintering in sugar-beet 

 top material varies according to the environment. When exposed to out- 

 door conditions the conidia die in one to four months; but when kept dry 

 they live as long as eight months. The sclerotia like bodies, which are more 

 or less embedded in the tissues of the host, are more resistant than the co- 

 nidia, living through the winter when slightly protected, for example, 

 in the interior of a pile of sugar-beet tops or buried in the ground at a depth 

 of I to 5 inches, and become a source of infection for the succeeding crop. 

 Notwithstanding the difference in temperature and soil moisture condi- 



