462 BOTANICAL GAZETTE [December 



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rounded by phloem (protostele.). Ordinarily, after the exit of a number of 

 monodesmi cleaf traces a mass of parenchyma makes its appearance in the 

 center of the tracheary tissue, which the authors regard as a true pith or 

 medulla. Gradually the '* pith " becomes enlarged as the young stem grows 

 stouter. Sieve tubes then make their appearance between it and the xylem. 

 Later still an endodermis is formed within the tubular stele (siphonostele), 



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but it is not clear from the author's description whether it originates in such 

 a way as to leave their primary "pith" in continuity with the fundamental 

 tissues of the true pith which finally shows itself within the fibrovascular 

 zone. It seems probable from the course of development observed in similar 

 instances that such is not the case. Sooner or later the. fibrovascular 

 ring becomes broken up into a zone of separate strands by the overlapping of 

 the gaps which occur above the exit of the leaf traces. Subsequently the 

 fibrovascular system is further complicated by the appearance of strands run- 

 ning through the pith and joining up the walls of the stelar tube just above 

 the points of exit of the foliar traces. The increasing complexity of the com- 

 missures leads to the extremely involved condition of the fibrovascular system 

 which is so characteristic of the adult marattiaceous stem. The authors were 

 unable to investigate the ontogeny of a third genus, Kaulfussia, but concluded 

 from the structure of the adult stem that the course of development of the 

 strands is probably the same as in Angiopteris and Marattia. 



They criticise the term phloeoferjna proposed by Strasburger to denote 

 the morphological boundary between the fibrovascular and fundamental tis- 

 sues, and point out with great force the fallacy of admitting the phloeotermal 

 value of the endodermal layer which surrounds n-\-\ fibrovascular strands, 

 and denying it where the endodermal zone surrounds only one such strand. 

 They conclude that the endodermis has no morphological value as a stelar 

 boundary, both on account of its inconstant occurrence and of the frequent 

 seriation of its cells with elements inside or outside the central cylinder. They 

 consider that the tracheary tissue is the only reliable basis for morphological 

 hypotheses, apparently losing sight of the fact that not unfrequently even the 

 tracheary elements themselves appear in seriation with endodermal cells, and 

 consequently, in accordance with the cell wall reticulum hypothesis, might 

 belong outside the stelar system. It appears probable that greater clarity of 

 view will supervene in developmental studies when with Sachs we cease to 

 regard the cell wall reticulum as having any greater importance than an 

 indication of the direction of the forces of growth. The morphological value 

 of a structural feature seems rather to depend on its presence in older groups 

 and in the young individual of higher groups, etc., than on histogenelic 

 details which are extremely unstable in both animals and plants. Incon- 

 stancy of occurrence appears further to afford an argument rather for than 

 against the ancestral character of any given morphological feature. It may 

 consequently result that Strasburger's conception of a pbloeoterma marking 

 the boundary between the stelar and fundamental tissues will ultimately be 



