598 INSECTS AFFECTING VEGETATION 



the worst and be prepared to take such measures as are possible for 

 the control of the trouble and for preventing its spread. 



The disease is caused by another one of the small imperfect 

 fungi, known to botanists as Thielaviopsis ethaceticus. The fun- 

 gus is an extremely rapid growing one and forms spores in abun- 

 dance. Two kinds of spores are produced. There are first some 

 small linear to oval, hyaline to brown ones which are produced 

 inside the hyphal threads and are pushed out in chains. These 

 are called the micro-conidia. These develop very abundantly on 

 cut surfaces of affected sugar cane stalks, and perhaps also to some 

 extent imbedded in the tissue of the host plant. These spores are 

 blown, around to other cane by the wind or are carried by insects. 

 They germinate at the first opportunity and if they are .in contact 

 with another stalk produce the disease in it. 



Then the fungus produces some larger, thick-walled, dark- 

 colored spores, called the macro-conidia. These are borne in chains 

 at the end of the conidiophores, but they are not borne within the 

 fungus threads, as are the micro-conidia. These serve as resting 

 spores. According to Cobb, they do not germinate immediately, 

 but seem to need a period of rest. If a diseased cane is split, in 

 the matter of a day or so, the cut surface will become black in 

 color, due to the abundance of these spores. 



This disease gains entrance to the stalks of cane entirely 

 through wounds in the rind. These wounds may be due to the in- 

 jury of insects or they may be the cut ends of the stalks. After 

 the fungus has once gained entrance to the stalk it spreads very 

 rapidly, decomposing the cane tissue and killing the eyes. 



A stalk affected with this disease does not usually show on the 

 outside. The exterior of the rind may be perfectly sound in ap- 

 pearance, while the interior may be badly decomposed. On split- 

 ting the stalk, however, the disease can usually be told. If the dis- 

 ease has progressed to any extent, the center of the stalk will be 

 more or less decomposed. The sugar-containing cells have been 

 disintegrated, and the fibre-vascular bundles of the central region 

 will be seen to be more or less free. This central cylinder, or pipe, 

 as it is called, is generally nearly black in color. If the disease 

 has not progressed far, however, this black color may not be pres- 

 ent, but it will develop in a few hours if the split stalk is left in 

 a moist place, as this black color is due to the presence of the macro- 

 conidia. 



Then, if the whole stalk is not as yet affected, there will gen- 

 erally be a sharp boundary between the diseased and the healthy 

 joints. The fungus grows very rapidly through the internodes, but 

 is halted for a time at each node. Of course, the stopping of the 

 fungus by the node is only for a time. It soon is able to pass this 

 point and then rapidly grows through the next internode. 



Another characteristic point in regard to this disease is the 

 odor given off by the affected stalks. The odor is described as simi- 

 lar to that of ripe pineapples, and on this account it has received the 

 name of the pineapple disease. The disease does also affect pineap- 



