DISEASES OF VARIOUS CROPS I70g 



worst enemies of rice cultivation in Java; lo) « Omo Poetih », caused bj^ 

 Nymphula stagnalis or Cnaphalocrocis jolinalis, these insects attack the 

 leaves which they feed upon; to destroy them it is only necessary to flood 

 the rice plantations; ii) several other insects such as Cirphis unipiinctata^ 

 Psalis securis, Melanitis leda and some of the Hesperidae, which also feed 

 upon the leaves and at times do a good deal of damage; 12) Tinea sp. which 

 can lead to serious losses in stored rice; 13) Cecidoniyia sp. and another 

 Dipteran hitherto unidentified which sometimes attack the nurseries; 14) 

 Calandra oryzac, which attacks shelled rice; 15) among the mammals are 

 rats which can do a great deal of harm in the plantations, and birds alsc, 

 especially Munia oryzivora which is a perpetual source of danger, necessi- 

 tating a continuous watch being kept in the plantations when they are dry , 

 so that the intruders may be driven off. 



1230 - On the Reappearance of Mildew {Phytophihora infestans) in the Haulm 



of th3 Potato. — ERrK530N, T-i in Comptes rendus hebdomadaires des Seances de V Aca- 

 demic dcsSciences, Vol. 163, No. 4, pp. gj-ioo. Paris, 1916. 



The writer has drawn the following conclusions from his further in- 

 vestigations of Phytophihora in/estans : 



i) In the field the disease does not appear until 3 or 4 months after 

 the tubers are planted. In Sweden the first attack varies from the middle 

 of July to the end of September according to the weather. 



2) In the first outbreak of the disease which comes at the end of 

 the sunmier the leaves are seen to have large, distinct, black patches espe- 

 ciall}' the more vigorous ones which spring from the base of the plant, 

 at the same time the lower surfaces are covered with a fine greyish dust. 

 At the end of 2 or 3 days the black patches begin to invade the tubers. 

 Damp and misty weather encourages the growth of the fungus. 



3) Where the tubers are planted in frames in January the first tra- 

 ces of the disease appear in the middle of April when the stems and leaves 

 are fully developed. The tubers are at this time as well developed as are 

 those of field grown potatoes at the end of the summer. 



4) After the early appearance of the fungus in the tubers in hot- 

 beds the stems and the petioles are invaded and take on a greyish colour. 

 The petioles often become thread-like but the blades remain green without 

 showing any sign of the disease. 



5) On the first day several zones can be distinguished in the dis- 

 eased patches. Starting from the middle and radiating outwards there are: 

 a) a dark brown region verging upon black; b) a velvet}^ grey region; c) a 

 pale yellow region free from rust; d) a region of healthy dark green which 

 lies about 10 mm. away from b. 



6) In the dark green region and in the adjoining pale green part the 

 cells are normal, with nuclei, chlorophyll grains etc. Onh* the cytoplasm 

 of the cell differs from normal c>i;oplasm. 



With the help of powerful magnification the presence of black spots 

 in the plasma between the chlorophyll grains has been shown. No other 

 trace of the mycelium has been discovered either in the cells or in the ad- 

 joining .spaces. 



