THE SEREH-DISEASE OF SUGAR-CANE. 73 



The essential signs of the disease are not known. The following characteristics, how- 

 ever, are generally taken as signs of Sereh : 



(i) Shortening of the internodes of the stem, resulting, especially when this takes place toward 

 the top of the plant, in conspicuous crowding of the leaves into a fan-shaped mass (Kriiger, Valeton, 

 Went). 



(2) Leaves smaller than usual; they also remain longer on the plant and do not fall off in the 

 usual way. (Went, Kriiger). 



(3) Leaf-blades etiolated or traversed by yellowish-green stripes (Kriiger, Valeton, Went, 

 Benecke). They die irregularly in badly diseased plants. The ehlorophyl is not well developed 

 in the leaf-stripes. 



(4) The leaf-sheaths open out early and stand widespread, giving to diseased cane a clavate top. 

 Sound canes have narrowly cylindric tops, somewhat constricted above (Kriiger). Diseased leaf- 

 sheaths often die first at the midrib rather than on the margin (Went). 



(5) The starting of shoots and roots from nodes above ground (Kriiger, Valeton, Went). This 

 phenomenon may be induced also by flowering, borers, and lodging of the cane (Kriiger, Went). In 

 Sereh it is accounted for by a checking of the growth as a result of irregular sap-circulation due to a 

 plugging of the vessels with gum; by the persistency of the leaves on the stem; by the absorption 

 through the impaired stem of the water held in the leaf -sheath. 



In severely attacked Sereh-diseased plants the root elements, which one finds above every node, 

 sprout, and in this way the stem becomes surrounded by a net-work of by-roots (Went). 



(6) An abnormally strong stooling of the diseased cane, due to a sprouting of buds below the 

 ground (Kriiger, Went). 



These [the buds] are often swollen and in severely attacked plants sprout easily. The latter is 

 the case especially with the lower buds. The stems springing therefrom are also for the most part 

 attacked in turn, remain short therefore, the buds sprouting again and in that way exhibiting the form 

 of a typically severely Sereh-diseased plant, consisting of a bundle of low stems with a bush of leaves 

 (Went). 



(7) A weak and poor development of the root-system, especially in badly affected plants (Kriiger, 

 Went, Wakker). The roots are often dead at the ends; they may be much branched, but remain short. 

 This, however, is not a constant characteristic of badly diseased plants. Conspicuous external signs 

 are said to appear first on the parts above ground. Tschirch figures many short stumps of roots with 

 dead ends, but Kriiger thinks this may be due to nematodes. Went gives this as one of the signs. 

 According to Went, gum-diseased vascular bundles seldom occur in the roots, i. e., more rarely than 

 in the stem. 



(8) Inclination to bloom early (Went). This phenomenon appears conspicuously in plants not 

 too badly diseased. 



(9) The foliage of the plant dies gradually from below up (Kriiger). The top of the cane is less 

 diseased than the base, and it is advised to plant this part of the cane exclusively in the hope of obtain- 

 ing Sereh-free plants (Went). 



(10) The disease is carried over from old plants to young ones by means of cuttings (Soltwedel, 

 Valeton, Wakker, Went), especially in cuttings taken from the top of the stem (Kriiger), bottom 

 (Went). There is often rapid decay of planted cuttings when these have been taken from Sereh- 

 diseased cane; the decay is accompanied by a disagreeable odor and a red stain. Valeton says that 

 he has seen the disease appear within three months in shoots derived from affected cuttings. 



(11) A decided red stain in the vascular bundles of the stem. There seems to be a general agree- 

 ment among the writers on Sereh that this is one of the conspicuous signs of the disease. Went 

 declares it to be the only sure sign. In early stages it is said to be confined principally to the nodes. 

 Benecke says that this red stain is peculiar to Sereh. Kriiger says that while it may come more 

 quickly in Sereh it is also found in other diseases due to unfavorable conditions of theearth, etc. This 

 sign may be discovered first in the base of the plant in the stem and to a slight extent in the adjacent 

 roots. In the dead leaf-sheaths also, especially near the point of union with the stem, there are red 

 bundles, having their ducts filled with gum. 



In Sereh-diseased plants the lower end of the stem especially is wholly impregnated with gum- 

 diseased vascular bundles, which run in all directions, the entire tissue having become very tough and 

 giving the impression of having suffered through lack of water (Went). 



Valeton says: " I have examined Sereh-diseased canes 3 meters long, whose upper 46 nodes were 

 wholly free from gum and red color, " and also that " Plants descending from white tops [undeveloped 

 tops] on the contrary, are, after months, often wholly free from gum-formation." Went makes a 

 similar statement. Other authors mention the disease as sometimes appearing first when thecanehas 

 reached a considerable height, the lower internodes being of normal length and size, and only the 



