PECAN" ROSETTE. 17 



often showed marked signs of rosette the first year after trans- 

 planting. Trees in low situations where humus and fertility ac- 

 cumulate from year to year were almost always found to be uni- 

 formly vigorous and free from disease. Briefly stated, 90 per cent 

 of the cases of rosette were found under conditions indicating lack 

 of humus, plant food materials, and moisture. 



Fertilizer tests (50) showed in two years a marked improvement 

 in rosette cases and also many cases of [apparent] recovery. Stable 

 manure, particularly, gave excellent results. Rosetted trees in the 

 plat that received ground limestone at the rate of 3 tons to the acre 

 not only failed to improve but were more severely attacked at the 

 end of the third season following its application than at the be- 

 ginning. 



Examination of large numbers of trees (50) showed that the feed- 

 ing roots are distributed through the surface soil, and in proportion 

 as this is deep and fertile do pecan trees usually attain their normal 

 development and vigor. Long hot, dry periods often kill many of the 

 feeding roots in the shallow surface soils ; and deep sand, clays under- 

 lain by sand, and eroded hillsides were found particularly to favor 

 rosette. An acid soil, according to McMurran, is probably not the 

 cause, since river flood plains nearly all exhibit an acid soil, and 

 pecan rosette under these conditions is a rarity. 



EXTERNAL SIGNS OF ROSETTE. 



Every phase of the disease is observed on trees of all ages, from 

 young seedling or budded and grafted stock in the nursery row to 

 trees of long-established maturity. 



In every distinct case the constant sign of rosette consists in the 

 final development of undersized, more or less crinkled and yellow- 

 mottled leaves (Plate I, fig. 2; Pis. II to IV), particularly at the ends 

 of one or more branches. This phase may be properly designated as 

 the secondary stage of the disease. The chlorotic areas are situated 

 between the principal veins, while portions adjoining these veins and 

 along the margins of the leaflets are green. In severe cases these in- 

 tervascular chlorotic areas are thinner than in healthy leaves, while 

 along the midrib and principal veins the blade is often somewhat 

 thicker than normal. This condition gives the leaf a peculiarly rough 

 and furrowed appearance and causes the veins to stand out char- 

 acteristically. Such leaves do not attain their normal size, are 

 often linear (PI. TV) and otherwise malformed, and present a 

 crinkled or undulated appearance of the laminae. Parts of the 

 laminae are often suppressed ; sometimes the leaflet consisting merely 

 of the midrib bordered by an edging of ragged tissue. In laminae 

 otherwise fairly normal in general form, portions of the mesophyll 

 76289°— 22 3 



