2o6 DISEASES OF CROP-PLANTS 



Collar Canker. 



Lime trees up to four or five years of age, under conditions 

 where growth is slow and uneven, sometimes develop a rough 

 and swollen structure of the basal portion of the stem extending 

 for a few inches or up to a foot above the surface of the soil. 

 The cortex and bark are divided into irregular patches, and the 

 new wood is deposited in lumps and ridges. Open wounds 

 may extend to the wood, and frequently matters are complicated 

 by infestation with the lime bark beetle, Leptostylus prcemorsus, 

 which begins on the damaged spots but extends for some distance 

 under the healthy bark. The trees make a persistent struggle 

 against the condition, but not infrequently die from the girdling 

 of the stem. Wounds on the roots such as are described by 

 F. W. South in connection with this affection are caused by the 

 larvae of Diaprepes or Exophthalmus weevils and have no 

 relation to the disease. 



The origin and nature of the disease are not known, and no 

 parasitic organism has so far been found to be at all constantly 

 associated with it. It appears to be connected with somewhat 

 impoverished or insufficiently drained soils, and is in the end 

 overcome by attention to these matters and by the trees which 

 survive outgrowing the trouble. 



Branch Galls. 



In one section of Jamaica there is a disease of lime and orange 

 trees, more severe on the first named, which was originally 

 reported in the following terms : " The lime trees are infested 

 with galls, which in some instances appear to do as much harm 

 as the scale insects. The galls are found on old and young trees, 

 but usually they grow first on fairly old limbs. These limbs 

 then send out strong young shoots for a time, but speedily get 

 exhausted and die, large numbers of limbs dying until many fine 

 trees are killed, or so nearly so as to be useless." 



Causation. 



The disease was investigated by L. S. Tenney and F. Hedges, 

 who found that a fungus Sphceropsis tumefaciens Hedges, could 

 be detected in the galls and that it reproduced the disease when 

 inoculated into healthy trees. 



When present in quantity the mycelium imparts a black 

 appearance to the tissues, but frequently only small amounts are 

 present. The fructifications have been found by S. F. Ashby 

 in abundance on branches near the galls. They are in the form 

 of solitary or congregated sub-spherical pycnidia covered at first 

 by the epidermis, and emerging later, producing oblong or ovoid 

 spores, rounded at one or both apices, or sub-acute, sometimes 



