The Morphology of Ruppia Maritima. 127 
2. The hydrophytic adaptations of the shoot are as follows: first, 
in its external form it shows a weak, wide spreading branch system, 
with slender stems and long grass-like leaves; second, in its internal 
structure, it reveals a thin-walled epidermis, photosynthetic and 
without stomata, in the leaves, a production of slime by the axillary 
scales for protective purposes, a copious internal development of 
air spaces, a complete lack of mechanical tissue and a reduction of 
the vascular system to a single main axial bundle and two small 
lateral bundles in both stem and leat. 
3. The hydrophytic adaptations of the root are as follows: first, 
in its external form, a reduction of the root system to small, un- 
branched, adventitious roots, borne singly at the nodes, and the 
formation of a protective coleorrhiza ; second, in its internal structure, 
the presence of numerous air spaces and the reduction of the 
vascular system to a single, axial, concentrically arranged bundle 
similar to that in the shoot. 
4. The characteristic adaptations of land halophytes are wanting 
here, for the reason that their cause, the need for reduction of 
transpiration, is lacking. 
5. Ruppia shows, however, a remarkably interesting halophytic 
adaptation in its power to live in salt water, which, when applied 
to submerged fresh water plants, causes instant plasmolysis. 
6. This salt water is not equal in strength to that of the open 
ocean, containing in New Haven Harbor, about 2.8 per cent of salt, 
and may therefore be termed “brackish”. 
7. My experiments show also that this power is confined to 
a very slight margin, 1. e., that slightly concentrated harbor water 
causes plasmolysis in both root hairs and leaf cells of Ruppia prov- 
ing that the plant, as now constituted, could not exist in ocean 
water. 
8. The tracheae and cortical bundles are evidently more or less 
rudimentary and possibly represent useless structures handed down 
by heredity. 
