Abstract
1. An explanation is offered for the apparently anomalous composition of the xylem of the stem in Zamia and Stangeria. 2. It is shown that although the stem wood of tuberous species of Zamia does not pass beyond the scalariform stage, certain trunk-producing species from Central America show abundance of tracheids with circular bordered pits. 3. The presence of circular pits in the tracheids of the leaf rachis is hence explained; otherwise the occurrence of pits would constitute an exception to the doctrine of conservative organs. 4. The tuberous species of Zamia are regarded as persistent juveniles with respect to their growth habit and their xylem; that is, they remain immature vegetatively although they reproduce freely. 5. A comparison is made between these juvenile cycads and such persistent juveniles as the Retinispora species and other conifers. 6. A similar explanation is considered to apply to Stangeria. 7. All organs of the cycad plant are surveyed in order to test the validity of the explanatio...
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