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BOTANICAL GAZETTE 



[OCTOBER 



forming triaxial tracheae which are in contact at the three points 

 with the tissues of the three plant regions. 



The young stem directly above the foot attachment contains 

 xylem elements which are relatively short and grouped in a typical 

 protostelic manner. They are surrounded by a single layer of 

 nucleated parenchyma cells, external to which a few sieve tubes 

 are disposed in a much broken circle. These are succeeded exter- 

 nally by a pericycle layer one cell in width, and which, like the 

 phloem, is more or less discontinuous. Frequently an embayment 

 occurs in the xylem at the edge of the foot attachment with the 

 stele (fig. 6). This is occupied by parenchyma which is usually 

 continuous with that of the root which lies between the protoxylem 

 points, and extends up into the stem, where it usually becomes more 

 shallow, and is exserted before the departure of the first leaf or 

 soon thereafter. This indention, when present, occurs at right 

 angles to the plane of the foot attachment and never in the position 

 of a gap (fig. 32). 



The first leaf trace is detached from the stele about 70-150 /x 

 above the foot, and is preceded by the appearance of 1-3 paren- 

 chyma cells in the xylem, which assume an eccentric position 

 beneath the place of leaf exit. Quite commonly these first cells 

 are in contact laterally with the sheath parenchyma; but whether 

 in contact below or not, they become confluent with the sheath 

 parenchyma at the time of exit of the first trace, when the xylem 

 of the stele once more forms a solid group. It is quite evident, 

 therefore, that this first xylem parenchyma is merely an accom- 

 panying feature of the departure of a simple trace from the pro- 

 tostele. Very similar to the preceding is an unusual behavior 

 observed when an embayment of parenchyma at the foot attach- 

 ment became decurrent in the xylem of the root. This par- 

 enchyma cell could not be shown to be in contact with that 

 surrounding the xylem, but apparently was lost in the midst of the 

 metaxylem elements of the root, just as the decurrent paren- 

 chyma associated with the departure of the early traces in the stem 

 may end blindly in the tracheae a short distance below. 



DeBary (3) considered the stele of the Osmundaceae as a 

 sympodium of leaf traces, and, in reference to the young stem, 



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