'2.2'J 



Tropical Plants. 



In consideration of my standpoint, that in much of our cultivation too 

 Httle account is taken of the soil conditions, especially of its physical consti- 

 tution, I think it necessary to refer also to the demands of tropical plants on 

 the physical peculiarities of the cultivated land. In regard to tropical plants, 

 I base my theory on the statements of Fesca^ who has often given his own 

 experiences, and further, on the recent publications of the Biological Agri- 

 cultural Institute at Amani-. 



As we shall see, in these injuries, as in those in temperate climates, 

 phenomena are often involved which are due to scarcity of oxygen mani- 

 fested in heavy soil or in soils which have become compacted through culti- 

 vation. Many plants in the tropics can develop accessory organs with a scar- 

 city of oxygen, like the adventitious roots from the trunks of trees buried or 

 covered with slime. The palms (Phoenix, Kentia, Chamaerops etc.) car 

 develop root branches growing perpendicularly out of the soil which have a 

 peculiar respiratory arrangement (Pneumathodes) ; this appears as a mealy 

 coating extending backward for a certain distance from the tip of the root. 

 This mealy condition is produced by the increase, enlargement and breaking 

 up of the outer layers of the rootbark with a rupturing of the epidermis and 

 an almost complete suppression of the schlerenchymatic ring, Jost^ deter- 

 mined experimentally with Phoenix that these pneumathodes remain in the 

 soil when it is well aerated, but, on the other hand, are raised above the sur- 

 face of the pot if it is submerged in w^ater. Similar arrangements were 

 found also in Pandanus, Saccharum and Cyperus. 



Root-Rot of the Sugar Cane. 



Among the numerous diseases of sugar cane, root-rot plays a prominent 

 part. In Java it is considered the worst enemy of sugar cane culture. Nat- 

 urally growers have not failed to cite the micro-organisms (Verticillium. 

 (Hypocrea) Sacchari, Cladosporium javanicum Wakker. Allentospora rad- 

 icicola, Wakker, Pythium etc.) colonizing on the diseased roots as its cause. 

 Nevertheless Kamerling's* recent experiments have now confirmed beyond 

 all doubt the supposition that a constitutional disease is concerned here, 



1 Fesca, Der Pflanzenbau in den Tropen und Subtropen. Berlin Siisserott. Vol, 

 I, 1904. 



2 As said above, the statements on the phenomena of disease in cultivated 

 tropcal plants serve chiefly as proof of the necessary consideration of soil and at- 

 mospheric conditions as a cause of disease. In the descriptions we can sum up the 

 material more briefly since abundant literature easily makes possible special 

 studies. Besides the magazines already mentioned, pp. 65 to 67, the recent publica- 

 tions of the Usamtaara-Post furnish valuable material. "Der Pflanzer," Adviser for 

 Tropial Agriculture" issued with the co-operation of the Biological Agricultural In- 

 stitute, Amani, by the Usambara-Post, 1905. ("Der Pflanzer," Ratgeber fiir tropische 

 Landwirtschaft unter Mitwirkung des Biologisch-Landwirtschaftlichen Institutes 

 Amani, herausgageben durch die Usambara-Post, 1905.) 



3 Jost, Ein Beitrag, zur Kenntnis der Atmungsorgane der Pflanzen. Bot. Zeit 

 1887, No. 37. 



4 Kamerling, Z, Verslag van het Wortelrot-Oenderzoek, Soerabaia, 1903, 209 

 pages, with 19 Plates. 



