254 Journal of Agricultural Research vol. xx, no. 4 



On the small roots the hypertrophied lenticels occur most commonly, 

 but not always, at the junction of a lateral root or rootlet with its parent 

 root, usually originating immediately above the point of origin but also 

 subtending, at the sides or immediately below, the root or rootlet in 

 question. This agrees with the findings of De Vaux (5) 1 on normal lenti- 

 cels, who reports that primary lenticels on roots are always at the bases 

 of root branches, though secondary lenticels are sometimes formed later 

 at other points. It was this coincidence of lenticels and root branches 

 that caused some botanists during the early part of the nineteenth 

 century to believe lenticels equivalent to buds, a doctrine attributed to 

 De Candolle (7; 13, Vorwort) and overthrown by Majer (13), 2 Unger (22), 

 Terras (19), and others. 



The excrescences vary greatly in size and shape, from minute circular 

 areas 0.5 mm. in diameter to bands nearly encircling the larger roots in 

 cases where two or more lenticels have become laterally confluent. 

 Around the root crowns and the bases of the submerged stems large, 

 wartlike patches may occur, 5 to 8 mm. in diameter and projecting 1 to 

 3 mm. above the surface of the bark. Examination with a dissecting 

 microscope shows these excrescences to be made up of a very loosely 

 piled mound of pale yellowish tissue. As a general rule these mounds 

 of loosely piled cells split in a stellate manner, the segments recurving out- 

 ward, occasionally leaving a few filamentous columns standing by them- 

 selves in the center. Such structure is evident only when the young 

 trees have been removed from the ground with great care, for the slightest 

 touch upon these loose-lying columns causes them to crumble instantly 

 to a flat, powdery mass, especially when they are dry. On the bases of 

 still older stems 1 to 2 inches (2.5 to 5 cm.) in diameter that stand for 

 a large part of the growing season in water or poorly drained soil, the 

 bark, which is here considerably thickened, exfoliates in patches of varying 

 size, revealing irregularly connected flattened masses of cells, or, more 

 rarely, unbroken areas of such cells 1 inch (2.5 cm.) broad. On some 

 pines these excrescences frequently become so abundant that con- 

 siderable areas of the lower stem and the tap root are covered by them 

 (PI. 46, B). After the cessation of growth in the lenticels, these excre- 

 scences become dark root-brown and gradually slough off. 



The lenticellular excrescences vary in different conifers from loosely 

 connected, more or less divergent, columnar masses crumbling at the 

 slightest touch, common in the pines, to fairly compact, corky masses 

 usually seen in the trees of other coniferous genera. 



Histological examination of the excrescences at once proves the white, 

 spongy tissue to consist of more or less loosely connected masses of cells 

 developed from the phellogen. Plate 44 illustrates a cross section of 



1 Reference is made by number (italic) to " Literature cited," p. 264-265. 



2 This seems to be the 1836 paper attributed to Mohl by Haberland (7). Mohl apparently directed the 

 work of Majer and wrote a preface for the dissertation, but Majer was the author of the paper itself. 



