228 



resulting from compacting the soil. Raciborski with Suringar' has expressed 

 the theory, earlier proved, that by transplanting sugar cane, which had suf- 

 fered from this root disease, known as Domikellanciektc, to oilier soil, the 

 I>lants would become healthy. The disease occurs especially on heavy clay 

 soils and manifests itself in Java, when at the beginning of the spring mon- 

 soon the plants die with alarming rapidity after they have already shown for 

 some time an abnormal branching of roots and also deformed root hairs. He 

 investigated the soils in which the disease occurred and found that they did 

 i/ot have sufficient friability and easily became compacted. The permeabil- 

 ity of the soil can be increased by supplying humus, since this, as also ferric 

 hydroxide, or silicate rich in iron, favors the formation of friable soils. Since 

 the humus is gradually lost by oxidation, care must also be taken to retain the 

 porosity of the soil by a renewed supply of stable manure, rice straw or 

 green fertilizer (compost). 



According to Wakker's- studies, many leaf spot diseases seem either 

 directly produced by moisture in the soil (if of a parasitic nature) or favored 

 by this moisture. Wakker found in the vicinity of Malang "a yellow streak- 

 ed, banded disease," "rust," "ring spot disease," as well as the red and yellow 

 spot disease. While he considers the first named as a parasitic phenomenon 

 favored by moisture, he explains the yellow spot disease, in which the leaves 

 acquire somewhat elongated, greenish yellow spots running into one another, 

 as a hereditary constitutional disease. 



Diseases of Cotton. 



The majority of the cotton diseases may be considered at present to be 

 of parasitic origin, but I doubt if this will always remain the case. With the 

 conviction that many of the micro-organisms already found are to be con- 

 sidered parasites of weakness, naturally the first existing factor must be 

 considered as decisive, viz., the disturbance in nutrition causing the weak- 

 ness which first offers the possibility of infection by the fungus. This will 

 have to be sought primarily in weather and soil conditions. 



Examples of disease, in which only the soil is considered as the cause 

 in the rainy season, are reported by Vosseler'" from our East African col- 

 onies. In 1904, in the district of Kelwa, there occurred a "browning of the 

 stems," which produced greater damage in that region than all the other 

 diseases which had appeared up to that time. Brownish black spots were 

 produced in the bark below the tip of the main shoot, as a result of which 

 followed the dying of this part as well as of the upper lateral shoots. The 

 disease appeared, however, only on so-called sour soil. 



1 Kamerling-, Z., en Suringar, H., Oenderzneking-en over onvoidoenden sroei en 

 ontijdig Afsterven van het riet als gevolg van wortelziekten. Mededeelingen van 

 het Proefstation vor Suikerriet en West-.Java, No. 48; oit. Zeitsohr. f. Pflanzenkr., 

 1901, p. 274, and 1904, p. 88. 



2 Wakker, J. H., De Bladzeikten te Malang. Archiev voor de .Tava-Suikerindus- 

 trie, 1894. Aflevering 1. 



3 Vossler, Zwei Baumwollkrankheiten. Immune Baum^jvollsorten. Mitteil. 

 Biolog.-Landwirtsch. Institut Amani, 1904, No. 32. 



