STOKEY— ANATOMY OF ISOETBS 3 2 7 



..oodle (,), in his account of the secondary thickening in the -o.s 

 „f Opossum vulgatom, figures both a cross and a long, udmal 

 section of secondary tracheids, which he describes respect.v ) as a 



developing tracheid with its protoplasmic contents an as • 

 ■longitudinal section showing part of the xylem with one de o W 

 tracheid containing protoplasm and a nucleus." In both the ca s 

 the tracheid character of the cell is too pronounced to be questioned 

 In ,he ease of Angiopieris evecta, Hill (14) says with reference to he 



condary growth: "Semi-ligni fieri elements with protoplasms 

 terns are found on the inside of the meristem." „„„.;,i n . 



II seems strange indeed, that while, in the case of other per 

 phues, i« is taken as a matter of course that tracheids may r ta.n^art 

 of their protoplasmic contents and appear in various stages 



ment, in Isoetes the same condition has been looked upon as 

 perable objection to the tracheid character of the cells in questi . 

 is obviously much more natural to interpret this tissue ^^.^ 



arreted development, than to regard it as anything so ex r 



! 1 1 -tv. a fart that we nna ca^-s 



as a combination of xylem and phloem. The fact n ^ 



of immature and imperfectly developed -f«^Sto than Is 

 pteridophytes is more enlightening as a basis of intcrpre ^^ 

 the presence of anomalous secondary thickening in 



Draraena - • ftfe ratted tracheids, 



The irregular disposition of the thin areas in the pn ^ ^ ^ 



' le not usual in the pteridophytes, is probably ^"^ ^ on 

 has been supposed. Gwynne-Vaughan (ll),«» Ms ^q^^. 



the tracheae of ferns, calls attention to the irrcgulanU ^ tinct i v pitted 

 daceae, Botryopteris, and others, illustrating cases o ^^^^ ^ 



walls. 



the xylem of Hel 



with char 



— .jwui ui « » mtHiuuiiuLttvo «v . form" to those in 



acteristic bordered pits of an oval or even circular ^ in the 



which the pits assimilate to the more scalariform type ^ ^ ^ 

 majority of ferns." In Lycopodium in the priman ^ ^ ^ ^ 

 areas are mostly long and narrow, of the scalariform^ y^ ^^ & 

 ^nder tracheids thev mav be round or oval, gi vmg ^ ^^ q{ 

 pitied or pitted appearance. A study of the api ^ ^^ ^ 

 L >copodium affords an opportunity for a compare. '_' j^ on 

 J^ttg tracheids, a comparison which is of interest as 



