Anatomy of Spartina Townsendii . 343 
castings scattered over these parts of the plants. These were often from 
x to 2 mm. long, occurring over the hydathodal lines and only on the living 
parts. On examination they proved to be heaps of cubical crystals, mainly 
of sodium chloride. Rapid evaporation after exudation had enabled the 
salts to crystalize out, and their accumulation in such castings had been 
favoured by a continuation of dry weather and the failure of the neap tides 
to submerge the upper portions of the plants for a few days. The worm- 
casting-like form of the heaps of crystals, their distribution on the plant, and 
their absence from withered or dead portions prove conclusively that they 
were products of excretory activity, not the remains after evaporation 
of clinging drops of water or spray. What is most surprising is the amount 
of salts excreted by these small structures. 
A shoot of Spartina with several leaves, when cut off under water and 
then transferred to a bell-jar with the cut end dipping in water, shows 
practically as great an excretion as potted plants placed in similar atmo- 
spheric conditions. The cut ends of the vessels are immersed freely in the 
water, continuity with the supply being secured without the intervention of 
an active cortical tissue as in the roots. The position of the most active 
of all the hydathodes in the stellate spongy chlorenchyma, with a thin layer 
of the same between them and the water-storing cells, precludes the 
possibility of much local pressure outside the hydathodes themselves. This 
would seem to throw the onus of their activity upon their own structure 
and contents, inducing the belief that the excretion is due mainly to some 
form of protoplasmic activity. 
When the plants are submerged, some such system is necessary to get 
rid of excess water and salts, and prevent flooding of the air-spaces. A simi- 
lar danger must be met even when they are exposed by the fall of the 
tide, for the cushion of air, held by the dense vegetation belt over the 
moist substratum, is more saturated than the atmosphere immediately 
above, with the result that transpiration is lessened and an auxiliary 
method of water-excretion rendered necessary. This is found in the system 
of hydathodes, which also enables the plant to throw off immense stores 
of salts. 
Rhizome and Culm . Both the underground and aerial shoots conform 
to the usual grass type. One distinctive feature, associated with the habit 
of the plant, is the development of air-passages which in the former are 
large, and separated by radial parenchyma plates only one or two cells in 
thickness, while in the latter they are smaller and separated by much 
thicker radial walls. Usually they arise by the development of stellate 
tissue, and its subsequent disruption ; sometimes large rounded cells break 
down without any appearance of stellate cells. 
Leaf. The leaf also shows few variations from the normal furrowed 
grass type, except in the epidermal characters already described. Forty to 
A a 2 
