ABSTEACTS: PHYTOPATHOLOGY 29 



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The bacteria thrive only in the meristematic tissues which are Httle 

 or not at all lignified. Stomatal infections are common on the young 

 tissues. 



Birds and insects are believed to be carriers of this disease. It is 

 recommended that badly diseased trees be cut down and burned. All 

 fallen leaves, nuts, etc., should be removed. 



Erwin F. Smith. 



PHYTOPATHOLOGY. — A knot of citrus trees caused by Sphaeropsis 

 tumefadens. Florence Hedges and L. S. Tenny. Bulletin 247, 

 Bureau of Plant Industry, U. S. Department of Agriculture. Pp. 

 74, pis. 10 and figs. 8. 1912. 



This bulletin describes in detail a new fungous disease of citrus trees. 

 Branches of lime and orange trees affected by the disease were first 

 received from Jamaica, but recently a knot on a lime twig was received 

 from Florida, w^hich very much resembles the Jamaican disease, and is 

 probably the same. From the Jamaican material a fungus, Sphaeropsis 

 tumefadens Hedges, has been isolated which reproduces the knots when 

 sound lime and orange trees are inoculated with pure cultures. Many 

 successful inoculations have been made with reisolations from these 

 artificially produced knots. 



The first indication of infection is a slight swelling of the branch. As 

 this increases in size the bark, which at this stage covers the young knot, 

 becomes lighter in color and is noticeably cracked and has a cork-like 

 appearance. Growth under greenhouse conditions in Washington is 

 slow, several to many months being necessary for the production of 

 knots 1 to 3 inches in diameter. As the disease develops, secondary 

 knots form on the main branches and trunk, often extending to the 

 ground, and the death of the entire tree is the ultimate result. 



The mycelium of the fungus may occur in any or all of the tissues of 

 the stem, being particularly abundant in the cortex and wood. Large, 

 rapidly-growing knots as a rule contain less mycelium than the smaller 

 slow-growing ones. In young, rapidly-growing tissues of buds growing 

 out of knots the mycelium is confined to the intercellular spaces. 



The fungus is easily isolated from the knots, fresh young knots being 

 preferable for this purpose. It has also been isolated from the stem 

 between the knots. 



The pycnidia as they have been observed upon the host are subglo- 

 bose, papillate, very dark brown or black, ostiolate, closely crowded 

 together or solitary, with a cellular peridium, and measure 152 to 224 



