RENNERT: THE PHYLLODES OF OXYPOLIS FILIFORMIS 407 
polts does not owe its peculiar structure to an adaptation to wet 
and dry periods, but that it is a true swamp or bog xerophyte in 
accordance with the generalization of Schimper, who supposes that 
the water of bogs and swamps contains such a large proportion of 
humic acid as to render absorption difficult. Plants growing in 
such places therefore have difficulty in securing a requisite supply, 
as if growing under arid conditions. Not all plants are capable of 
absorbing water from a mixture exhibiting a higher pressure than 
that of the cell-sap of the absorbing organs. 
Dr. Shaw * has pointed out that the vegetation of a pond in 
its final stage is always xerophytic and has drawn attention to the 
fact that the continual deposit of organic material around the mar- 
gin of a pond will produce a zone so much filled with humic acid 
as to be entirely devoid of vegetation. Dr. Cowles} has upheld 
this view of the xerophytic character of an undrained swamp and 
has frequently noted the remarkable assemblage of xerophytic 
adaptations such as leathery or hairy leaves and special structures 
for water absorption exhibited by the flora of peat bogs. In con- 
firmation of this standpoint Dr. Cowles has pointed out that if 
plants growing in swamps of this type are xerophytic we ought 
to find them thrving in dry regions. And this he reports to be 
true; Clethra alnifolia, Spiraea tomentosa and Myrica cerifera, gen- 
erally conceded swamp plants, have been found thriving and in 
all respects normal on dry hillsides. 
As Briquet has indicated, the most superficial examination of 
the plant brings to light the unmistakably xerophytic character of 
the reduced leaf-surface and the strong development of hypoderm. 
On the other hand many of the characters which Briquet regards 
as demonstrating the hydrophytic nature of the plant, seem when 
viewed in the light of recent ecological work, to be adaptations 
either for water storage or the prevention of transpiration. The 
large thin-walled empty celled endoderm certainly exhibits capac- 
ity for water storage. The thick cuticle and the waxy incrustation 
of the epidermis, the accessory cells and the sunken position of 
the stomata, and the presence of resin glands all point to the con- 
*Shaw, C. H. The Development of Vegetation in the Morainal Depressions of 
the Vicinity of Wood’s Hole. Bot. Gaz. 33: 437. 1902. 
¢ Cowles, H.C. Bot. Gaz. 27: 293. 1899. 
