THE SEREH-DISEASE OF SUGAR-CANE. 75 



Sereh has been ascribed to : 



(i) Unfavorable conditions of the soil, poor or defective working of the soil. It is much worse on heavy clay than on 

 lighter soil (Went). 



(2) Degeneration of the plant, or atavism. 



(3) Abnormal weather conditions, such as great dryness, too much rain, excessive water through improper drainage. 



(4) The use of unsuitable fertilizers, especially ground nut-cake. 



(5) The use of affected plants and unsuitable methods of planting, i. e., too deep planting, too late planting, too high 



heaping up of the earth. 



(6) Lack of water through dying of the roots, and the formation for this reason of gum in the bundles (Wakker). Sereh 



is not due to any parasite and is not infectious (Wakker). 



(7) Animal or plant parasites: 



(a) Root parasites, i. e., nematodes: 



(1) Heterodera (Treub). 



(2) Tylenchus sacchari and Heterodera radicicola (Soltwedel and others). 



(b) Bacterial stem parasites (Kriiger, Janse, Valeton). 



(c) Root and stem parasites, Pythium, nematodes (Treub). 



(d) Leaf-sheath parasites, especially Hypocrea sacchari, associated with root-parasites (Went). The Sereh 



disease is an infectious disease (Went). 



(e) Unknown parasites favored by special receptivity of a portion of the canes (Zeijlstra). 



Dr. Went says in one place in so many words : " The Sereh disease is caused by a disease 

 of the leaf-sheaths of the cane" (1893), but in other places he speaks more cautiously of 

 Hypocrea as a "presumptive cause, " and in still other places as a cause acting in connection 

 with root-parasites. He has now, I believe, abandoned this view. 



Kriiger does not think nematodes are the cause from the following facts : 



( 1 ) Typical Sereh may occur in plants which show no nematodes ; 



(2) With planted cuttings from different parts of a cane subject to quite similar conditions, the 

 most different grades of the disease may be obtained; and, 



(3) Canes may occur which are diseased in the upper parts, but not in the lower. 



Kriiger concludes that Sereh is a stem-disease, and certainly a disease of the vascular 

 bundles. He conjectures that it is a vascular bacteriosis. He states that it is a disease of 

 the bundles caused by bacteria, and arises from a plugging of the tissues with gum, which 

 prevents them from fulfilling all their functions. As a result of this plugging they develop 

 the signs of the disease the red bundles with their sheaths filled with starch, the dying of 

 the leaves, cessation of growth in the attacked parts, the abnormal stooling, and the starting 

 of aerial roots and shoots. Valeton, however, says there is no starch, or but very little in 

 the endodermis in the lower parts of diseased plants as compared with that in healthy canes. 



Janse ascribed Sereh to a new spore-bearing schizomycete, Bacillus sacchari, which is 

 often accompanied by another spore-bearing species, Bacillus glagae. He spoiled his hypo- 

 thesis, however, by finding the organism everywhere in normal cane, and also in many other 

 monocotyledonous plants, and in some dicotyledonous plants. As a result, therefore, he 

 was forced to the conclusion that the parasite occurs in a latent form in all the cane-plants 

 of Java and was not able to explain why it sometimes produced the disease and at other 

 times did not. The most that he seems to have proved is that there occurs quite commonly, 

 either on the surface of the nodes of the cane-plant or in leaf-traces entering these nodes, one 

 or more spore-bearing bacteria resistant to boiling water. These developed quite constantly 

 on sections of the nodes previously treated in this way, and he showed that they were not 

 derived either from the air or water. 



Valeton repeated Janse's cultural experiments. In his paper on the bacteriological inves- 

 tigation of cane varieties, Valeton describes his experiments to determine whether Janse's 

 organisms were present in healthy cane-stems in eastern Java. He experimented in the 

 same manner as Janse, having learned the method from him. The surfaces of the cane- 

 stems were treated with disinfectants or boiled, then cut open and incubated for 24 hours or 

 longer. In nearly all cases he got the same results and reached the same conclusions which 

 he now declares to be worthless (letter to the writer). He tested healthy canes of 42 vari- 

 eties of Saccharum officinal urn and of 3 other species Glagah(Saccharitm spontaneumltixm.) , 

 Glongong (5. soltwedel i Kobus), and 5. ciliatum Hackel. 



