64 



DISEASES OF CROP-PLANTS 



" ufra " disease of rice in India, and appears to be confined to that 

 crop. 



The worms exist in a free-swimming condition in the water 

 which covers the fields, and ascend the outside of the plants when 

 the humidity of the air permits. They infest mainly the leaf-buds 

 at the tops of the shoots, the upper nodes of the stem beneath the 

 leaf sheaths, and the developing ears. In no case do the worms 

 enter the tissues, but puncture the epidermis and absorb the 

 juices so obtained. There is no evidence of toxic action. Severe 

 infestations lead to the ruin of the crops. 



X5 



After N. A. Cobb 



, \X200 



.x.750^ 



AJter N A Cobb After N. A. Cobb 



Fig. 16 Coconut Root Tig 17 Coconut Parfn- Fig. 18 Egg of Aphe- 

 wiTH Nematodes chyma with Nematodes lenchus Cocophilus 



Reproduction proceeds vigorously on the growing plant 

 and eggs and larvae in all stages are found mingled with the 

 adults in the leaf-buds and around the young ear. With the 

 drying out of the ripened plant the worms coil up in the upper- 

 most nodes and within the glumes of the ear, and become dormant. 

 In this condition they are returned to the soil, and await con- 

 ditions suitable for the infection of the succeeding crop. 



Tylenchus ribes, Taylor. 



This species infests the buds of black currant bushes in 

 England, ascending the stems on the outside during wet weather 

 in the same way as the rice eelworm. Reproduction takes place 

 within the bud and the worms collect there in visible cottony 

 masses containing many hundreds. The colonies dry out in this 

 situation, and the worms revive and migrate when moist con- 

 ditions are restored. Seventy per cent, of the worms have been 



