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Ethel N. Thomas. 
A. lomarioides shows a somewhat different state of affairs. 
Its vascular system consists of an irregular circle of bundles, whose 
existence obviously bears no relation to the leaf gaps. 
Conclusion. 
We see then that in the facts brought forward here, there are 
two distinct centres of interest. 
With regard to its vascular anatomy Acrostichum aureum 
presents us, perhaps, with the most complicated petiolar system, 
coupled with a solenostelic stem structure, which has yet been 
described. Nevertheless, the horseshoe curve upon which the 
continuous or broken leaf trace of the Polypodiaceae is constructed 
can easily be distinguished. 
This anatomical structure cannot be readily referred to the 
habit of the plant, for although the dictyostelic species first 
examined were all prostrate creeping forms, the erect growing 
species A. crinitum, which was obtained with some difficulty, proved 
to be dictyostelic also, and in all respects quite similar to the 
others. A. aureum, however, certainly differs from A. crinitum, in 
its infinitely more robust and bush-like growth, as in the possession 
of a solenostele, and massive, complicated leaf-trace. 
The consideration of the structure of this plant in relation to 
its mode of life, has shown as we should have expected, that it is 
the roots which are most modified. 
This modification is seen in the very abundant development of 
lacunar cortex and further in a somewhat stem-like vascular 
anatomy. Both these features are characteristic of the roots of 
the mangroves, and A. aureum therefore shows very strikingly how 
similar may be the response to common conditions, even in plants 
separated very widely from a systematic point of view. We have seen 
that the characteristics dwelt upon here, are, in addition features 
very common in fossil roots, particularly in those of Lycopsida 
affinity. We have here then a vascular Cryptogam, which,growing at 
the present day under swamp conditions, shows special characters 
which are common also in the roots of fossil plants. As far as it 
goes, this is in support of the theory that many of our fossils were 
swamp plants. Dr. Scott remarks in his “ Studies ” that the 
lacunar character of Calamite roots points to life in water or wet 
mud. From the great development of vascular tissue, the latter 
seems more probable. 
I cannot avoid the conclusion that very probably the upper 
portions of the roots of Acrostichum aureum are exposed, and may 
