230 



If the clay soil lacks sand, however, and becomes loamy, it is useless 

 for tobacco culture. The roots of the plant develop scantily and are often 

 deformed. The leaves are not of the right length and are of poor quality. 

 The mosaic disease appears a week or two after transplanting. The red, 

 atmospherically disintegrated soils of Ober-Langkat are pretty compact and 

 here the plants are squatty ; the leaves standing close above one another are 

 not especially thin while the mosaic disease occurs rarely. It only appears 

 exceptionally on the shoots which, after topping, develop sparsely. 



On dark soils rich in humus, tobacco has an enormous, well-proportioned 

 development; the very large leaves are dark green and thin. The mosaic 

 disease abounds. 



This disease scarcely, if ever, occurs on the peaty, porous, Paja soil, 

 which has a high water-holding capacity. The enormous leaves almost 

 never wilt in the soil containing much water, but are very thick and rich in 

 oil; with fermentation they become dark colored and are therefore not \try 

 valuable. On fresh Paja soil the mosaic disease cannot be produced even 

 by topping. 



Coffee. 



The tree, which of all our tropical plants deserves the most consider- 

 ation, coffee, is extremely susceptible to soil conditions ; although droughts 

 are not favorable and it likes best to grow in soil which even at a time of 

 drought keeps fresh, yet it withstands drought much better than too much 

 moisture. If, during the rainy season, it is covered with water for only a 

 few days, it becomes irretrievably diseased. A sufficient capacity for water 

 in the soil, combined with abundant aeration, is therefore its chief need. 

 Freshly cleared forest soil is found to be especially favorable for its culti- 

 vation. Black rust (swarte roest) and canker diseases (Natalkrebs and Java- 

 krebs) (Djamoer oepas) with their diseased cambium are probably physiolo- 

 gical disturbances introduced by unfavorable soil and atmospheric conditions 

 and result later in fungus attack. The Liberian coffee is said to be less sus- 

 ceptible to impervious soil than the Arabian, and flourishes where the latter 

 fails^ 



The leaf disease described by Zimmermann as "Blorokziekte"^ seems 

 to me also to belong here. The leaves develop convex, yellow spots. Later, 

 the epidermis ruptures on these spots and the cell contents turn brown. The 

 trees in Java, to be sure, are not killed by this disease, but their fertility is 

 greatly reduced. As the result of an excessive water supply, Zimmermann 

 observed'' the so-called "little stars," occurring rarely in Coffea liherica and 

 more frequently in C. arohica; i. e. blossoms which open prematurely when 

 incompletely developed and therefore remain sterile. The disease should 



1 Delacroix, G., Les maladies et les ennemis des cafeiers. II edit. Paris, Chala- 

 mel, 1900, p. 8. 



2 Teysmannia 1901, p. 419. 



3 Eenige Pathologische en Physiologische Waarneminger over KofRe. Mededee- 

 lingen uit S'Lands Plantentuin, LXVII. 



