No. 459.] ANATOMY OF CATALPA HYBRIDS. I29 
tive character. Thus the tracheids lie in two zones. In the 
outer zone the tracheids form disconnected tracts of variable 
form and extent, which are rarely connected by a narrow zone of 
tracheary tissue on the outer face of the growth ring. These 
tracts are neither radial nor tangential in disposition, but the 
resultant of these two directions, and as they project diagonally 

Showing vessels with numerous 
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4. T 
Fic. 8.— Catalpa bignonioides. Tangential section, X 61. 
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inward, they join with very small vessels which constitute the 
final phase of such structures in the summer wood. In the 
second zone of tracheary tissue, the tracheids form tangentially 
extended tracts of variable form and size’which are always con- 
nected with vessels of larger dimensions than those lying in the 
outer zone, and these tracts form an almost continuous series. 
