568 Journal of Agricultural Research voi. iv, No.e 



CONCLUSION 



On the basis of our present knowledge it is impossible to suggest the 

 original habitat of this nematode. In view of its habits, its known 

 distribution indicates that it is adapted to tropical and subtropical con- 

 ditions of widely different character. Its infestation of plants differing 

 from each other so widely as banana and sugar cane leads to the suspicion 

 that it may be another addition to the already formidable list of nematode 

 parasites which adapt themselves to a great variety of conditions. Its 

 presence in Jamaica suggests the possibility of its introduction thence 

 into Porto Rico and the southern portions of the mainland of the United 

 States, where it would probably find suitable host plants in the sugar 

 cane and might be expected to attack other plants. 



In one way this investigation of the anatomy of Tylenchus similis adds 

 materially to our knowledge of the group of Tylenchi to which it belongs. 

 For a long time observers have noted in this group the presence of puz- 

 zling tissues or organs near the base of the neck, and these have been 

 described and figured in a way that indicated a very incomplete and 

 unsatisfactory knowledge of their real nature; in fact, they have always 

 been regarded simply as constituents of the cardiac bulb. These re- 

 searches prove that in Tylenchus similis these peculiarities of the base of 

 the neck are due to the presence of a threefold gland emptying through 

 the lumen of the oesophagus near the base of the spear. 



What appear to be homologous organs are known in other genera and 

 are regarded as "salivary glands," admittedly more on the basis of their 

 structure than on the results of physiological tests. However, the mor- 

 phological evidence is very strongly in favor of the conclusions reached. 



The presence of such organs has not hitherto been noted in Tylenchus 

 or any nearly related genus. The details of the organ are difficult to 

 follow, but once they had been demonstrated it became evident that a 

 similar organ exists in other species of Tylenchus, and it is especially 

 interesting to note the presence of a similar organ in the well-known T. 

 dipsaci Kiihn, or, as it is yet more commonly known, T. devastatrix Kiihn, 

 the devastating nematode, so often responsible in the past for great dam- 

 age to bulbous crops, such as the onion and hyacinth. This similarity 

 in structure between T. dipsaci and T. similis makes it all the easier on 

 structural grounds to suspect T. similis of becoming a serious pest when- 

 ever it gets an opportunity. Whatever may be the cause, there is no 

 doubt of the ability of this species rapidly to break down the tissues of 

 the plants it attacks. One may now suspect, and on very good grounds, 

 that this ability is due not only to the battering action of the oral spear 

 but to the chemical action of a special secretion. Entirely in accord with 

 these ideas is the absence of this organ in the male of T. similis; when 

 the oral spear deteriorates, the gland deteriorates also. 



