324 HilL — On the Roots of Bignonia . 
ainsi formes : mais il y a neanmoins une penetration de 
1’ecorce dans le bois.’ It may, however, be stated that 
Bureau remarks that he had some doubts as to whether his 
plant was really Bignonia Unguis and not Stigmaphyllon ; he 
decided it was the former, on account of the character of the 
sieve-tubes. Judging from further remarks which he makes 
on the root-structure of this plant, it is very probable that 
his material came from a wrongly named specimen. De Bary 1 
states that he was unable to find the characteristic stem- 
structures in the roots of Bignonia capreolata. 
Van Tieghem 2 states at the end of his description of the 
stems of these plants : ‘ Les racines de ces memes Bignoniacees 
ne paraissent pas presenter ces anomalies.’ 
Before passing on to the root-structure of these plants it 
will, perhaps, be well to briefly describe the structure which 
obtains in the stem for the sake of comparison, 
Secondary thickening begins quite normally, as in other 
dicotyledonous woody plants. Sooner or later the develop- 
ment of secondary wood slackens very much at four points 
arranged cross-wise ; and as the secondary growth of wood 
at the intermediate portions of the circumference continues 
at the same rate as before, it follows that four depressions are 
left dipping down into the secondary wood : but inasmuch as 
the formation of phloem at these four points is increased in 
inverse proportion to the decreased formation of wood, it is 
obvious that the depressions are quite filled up with phloem 
as far as the outer limits of the bast, so that the general 
external form of the stem remains similar to that of an 
ordinary plant. These four phloem-wedges are very charac- 
teristic of many Bignonias. The cambium at the bottom of 
each depression still slowly forms xylem-elements, and in the 
cortex of the stem numerous sclerenchymatous masses occur. 
An essentially similar structure obtains in the root. In the 
ordinary root four phloem-wedges are found, and their 
development is identical with those of the stem. 
1 De Bary, Comp. Anat., Eng. ed., p. 573. 
2 Van Tieghem, Traite de Botanique, p. 823. 
