Nov. i6, 1914 Pecan Rosette 151 



In many cases the intervascular tissue here and there fails to develop 

 at all, so that the lamina is dotted with smooth-margined holes suggesting 

 insect perforations which have subsequently healed over (PI. XXV). 

 These first symptoms may occur over the whole tree at once, but often 

 one or more branches may be affected for several months before the whole 

 tree appears involved. At this stage the foliage as a whole often presents 

 a rusty appearance. The diseased branches usually fail to reach their 

 normal length, so that the leaves are clustered together on a shortened 

 axis, giving a bunched appearance to the group which led the senior 

 author, about 1902, to apply the term "rosette" as an appropriate name 

 for the disease (PI. XXVI; cf. fig. i, resetted shoot, with fig. 2, normal 

 shoot). Nuts are frequently borne and carried to maturity on these 

 branches. 



In some cases the disease goes no farther. The trees may continue in 

 this way for several seasons, or they may recover completely after show- 

 ing the early symptoms for one or more years. However, in a well-de- 

 fined case where the symptoms are general over the greater part of the 

 tree, the affected branches begin to die back from the tip during the lat- 

 ter part of the first season or later (Pis. XXVII and XXVIII). At 

 first brownish spots and streaks appear in the green bark, and these dead 

 areas increase in size until the whole end of the twig or branch dies. 

 While death appears to start in the green bark, the cambium soon be- 

 comes affected and the wood and pith are usually discolored. This 

 dying back or "staghorn" stage is followed during the same or the fol- 

 lowing season by the development of numerous lateral shoots from dor- 

 mant or adventitious buds. In young vigorous trees these first shoots 

 of the season are usually large and succulent, and the leaves are dark 

 green and above the normal in size. In all probability this effect is 

 physiologically equivalent to the effect of severe pruning. Toward the 

 middle of the season, however, the typical yellow-mottled color appears 

 and the later-developed leaves are more or less crimped and roughened, 

 as well as below the normal in size. Dormant axial buds of one or two 

 series may develop into abortive shoots, and toward the end of the sea- 

 son clusters of short or spindling branches usually put out from adventi- 

 tious or dormant buds farther back on the branches or on the main trunk. 

 The leaves in these cases are much reduced in size and may appear as a 

 mere skeleton with ragged edges. 



This process goes on from year to year. The growth of the tree is 

 checked, and these abnormal clusters of branches are formed only to die 

 back each season and be followed by others. Thus a well-marked case 

 of several years' standing presents a characteristically gnarled and for- 

 lorn appearance (PI. XXVIII, fig. 3). Rosette in all its forms occurs 

 in trees from seedling and budded or grafted nursery stock to trees of 

 long-established maturity, a hundred or more feet in height, and it is 

 one of the worst diseases known to affect pecans. 



