through Self- adaptation to a Moist or Aquatic Habit . 723 
phyte, in which the strands are scattered, is equally weak, 1 and snaps across 
with the greatest ease. 
Herr Ph. Eberhardt has shown how even a moist air has a similar 
effect to water upon woody stems, by greatly reducing the mechanical 
tissues of support. 2 Further illustrations will be mentioned later. 
5. Possible Aquatic Origin of Palms. 
Certain special resemblances are well illustrated by Palms. Though 
solid, silicified stems have been found fossil in Cretaceous rocks of America 
and in the Miocene of Antigua, some were remarkable for having a portion 
of the ground tissue in the condition of aerenchyma, a truly aquatic character. 
MM. G. Bonnier and Leclerc du Sablon illustrate this fact by a section of 
the stem of Palmoxylon lacunosum . 3 Mr. Drabble has also shown that 
many living Palms have roots full of lacunae, and names Kentia , Metroxylon , 
Phoenix , Caryota , Areca , &c., as well as Phytelephas . 4 
Another peculiarity about Palm-roots is the presence of what Jost 
calls ‘ pneumathodes ’. They are described as plaques farineuses , probably 
from some resemblance to lenticels ; they surround the bases of roots. 
M. C. L. Gatin, who gives an account of Jost’s paper, would refer them 
to something more analogous to what is found on Ferns of the orders 
Marattiaceae and Cyatheaceae (two of the most ancient kinds of Ferns), con¬ 
sisting of fine trees with noble fronds growing in moist ravines. He con¬ 
cludes his article as follows ‘ II ne me parait pas sans interet au moment 
ou les travaux de 1’ecole anglaise ont remis a Pordre du jour les importantes 
questions de phylogenie des grands groupes vegetaux, de constater une 
grande analogie de structure entre les organes respiratoires des Palmiers et 
ceux des Cyathceacees et des Marattiacees.’ 5 
Though most Palms have tall stems now , as terrestrial trees, it does not 
necessarily follow that primitive Palms were not small shrubs. 
Of course, pneumatophores are well known as occurring on the roots of 
hygrophytic trees and herbs, as Taxodiinn distichum , &c.; but they often 
fail to be produced if the tree grows in dry ground, as is the case with this 
deciduous Cypress. 
1 The rhizome, used as a drug, is known by the absence of a compact cylinder of xylem, which 
is replaced by stellate clusters. 
2 Ann. des Sci. Nat., tome xviii, 1903, p. 61. 
3 Cours de Botanique, p. 1214, Fig. 2193. 
4 The Anatomy of Roots of Palms. Trans. Lin. Soc., 2nd Ser., Bot., vi, p. 427. 
6 Observations sur l’appareil respiratoire des organes souterrains des Palmiers, par M. C. L. 
Gatin. Rev. G6n. de Bot., xix, p. 193. 
