10 THE RICE WORM (tYLENCHUS ANGUSTUS) AND ITS CONTROL 



southern part of the infected tract, rather later in the northern. At any 

 period during these months it is possible usually to find plants with numerous 

 worms actively feeding. Such worms when removed to water are intensely 

 active, swimming about with great vigour. In swampy ground, where a second 

 growth takes place from the stubble after harvest, this period may be, as 

 already stated, extended to February. But in the vast majority of cases, 

 the parasitic life ceases before harvest in late November or early December. 



At this period, as the host plant dries up in ripening, the worms cease 

 feeding, coil uj), and pass into a resting condition. The position on the plant 

 which they occupy after the ears emerge is the base of the peduncle, the stem 

 just above the next node lower down, and within the glumes in the ear. Here 

 they may occur in clumps or masses, visible to the naked eye as cottony tufts 

 or a grey coating on the surface of the affected parts, but they are often isolated 

 more or less completely and sometimes very scattered. The species is, there- 

 fore, less gregarious in its habits than appears to be the case with Tylenchus 

 ribes. Each worm usually forms a separate coil and the coil is usually quite 



circular (Fig. 1). The tendency to coil is a result 

 of desiccation as a rule, since at any time of 

 year coiling may be induced by drying out the 

 medium gradually. Occasionally coiling has been 

 observed to result from the action of weak 

 poisons, but the ordinary fixatives that are not 

 of rapid action usually kill the worm in an ex- 

 tended position, though there may be a short 



Fig. 1. Tylenchus angustiiii : . . , ., 



coiled indivi.iuai. preliminary tendency to coil. 



After coiling is completed, immersion in water leads to uncoiling. This 

 may happen even after the worm is dead ; at least it has often been observed 

 that old coils straighten out in water but undergo no further movement and 

 gradually decompose. The coiled worms are apparently protected in some 

 way (possibly by a mucous coating) from ready decay, and it has often been 

 extraordinarily difficult to decide whether a worm is alive or dead after placing 

 in water. Usually it is safest to rely on the resumption of active motility * 

 for determining that life persists. If the period of desiccation has not been 

 long, motility sets in soon after immersion, but after two months or more in 

 the dry condition it may take over an hour to commence, though uncoiling 

 is usually complete within the hour. To give a specific instance where doubt 

 remained as to the worm being alive, a double coiled worm that had been dry 



* By active motility is meant progression, or at least definite wriggling. 



