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SPARTINA GLABRA ASSOCIATION 39 
or gravel. For example, a series of soundings through the mud of the bottom, 
at different levels, along the main north-and-south axis, beginning at 2,700 
north, showed the following thicknesses of soft mud above the hard bottom: 
at the 6.5-foot level 5 cm. of mud; at the 6-foot level, 15 cm.; at the 5-foot 
level, 38 cm.; at the 4.5-foot level, 40 cm.; at the 4-foot level, 43 cm.; at the 
3-foot level, 70 cm. ; at 2.5-foot level, 66 cm.; at the 2-foot level, 36 cm.; finally, 
at the 1-foot level there was a thickness of but 30 cm. of mud above the firm 
subsoil. The thickness of the Spartina-bearing mud can be seen in the cross- 
section of this part of the shore of the harbor shown in figure 1. 
The rhizomes of the Spartina branch freely and run along more or less 
horizontally at about 1 to 1.5 dm. below the surface of the mud. The rhizomes 
are about 7 to 9 mm. in diameter and the living portion is about 2 or 3 dm. 
long. It consists of several or of many internodes, and may branch several 
times in its length. The terminal bud of the main axis maintains its horizontal 
position, while the lateral offshoots turn upward and give rise to the aerial 
shoots. From the base of each of these shoots a new rhizome puts out, in the sea- 
son after the leafy shoot is unfolded. By the network of interwoven rhizomes 
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Fic. 1.—North to south vertical section, at 0 east, of the Spit and adjoining portion 
of bottom, showing the depth of peat or mud overlying the gravel substratum, and 
the more important plants that dominate each level. Horizontal scale 1 = 3,000. 
Vertical scale 1 = 300. 
thus formed, which is in some places 4 or 5 layers thick, and by the roots which 
penetrate to still greater depths, the soft mud is firmly bound together for 2 or 3 
dm. below the surface. 
The aerial shoots push up above this substratum in the summer to a height 
varying from 1 to 2 meters, and sometimes have a diameter of 1.5 or 2 cm. at the 
base. In the denser stands of this grass there may be from 300 to 600 stalks per 
square meter. Hach aerial shoot may bear 1 or rarely 2 bladeless leaves at its 
base and 6 to 12 complete leaves toward the top. The size and general vigor of 
the plants differ greatly with the level of the soil in which they are rooted, and is 
usually greatest on bottom between the 3-foot and 6-foot levels. For example, 
Spartina growing on mud between the 3 and 3.5 foot levels, near 2,200 north 
by 600 east, is 15 to 20 dm. high, while other plants nearby, on soil at the 1.5 or 
2 foot levels, reach only 8 or 10 dm. in height. 
The flowers of some of the Spartina plants begin to open in the latter half 
of July, nearly 3 months after the shoots push up from the stubble in late April, 
but it is only the more vigorous plants, e. g., those on bottom between the 3 and 6 
foot levels, that begin to bloom as early as this. The smaller plants at lower and 

