40 THE RELATION OF PLANTS TO TIDE-LEVELS 
higher levels do not begin to bloom until much later than this, often in late 
August or even in early September. Apparently seeds are set rather freely on 
the stronger plants and a considerable crop of seedlings might be expected. 
As a matter of fact, seedlings are not very abundant, because, it seems, wnoc- 
cupied soil of the proper character and at the proper levels is not frequent. 
The seedlings that have been found in midsummer were growing on bottom just 
above the 1.5-foot level, that had evidently been disturbed by clam diggers (100 
north by 475 east), or by water-currents (2,000 north by 1,100 east and at mouths 
of Creek and rivulets), just at the time that the seeds were being dispersed by the 
water. This stirring of the bottom formed pits and furrows in which the seeds 
were readily buried.* Seedlings found at the first station mentioned, on July 1, 
1911, presumably from seeds ripened in 1910, were from 1 to 2 dm. high, had 
leaves, and a well-developed root-system, though the glumes were still attached. 
Our search for seedlings more than a year old was unsuccessful. All medium- 
sized plants examined proved to be young shoots at the tips of long runners from 
mature rhizomes. 
It is evident that the usual means of propagation and spreading to con- 
tiguous areas is by the longer branches of the rhizome. In this way the 
borders of a clump of Spartina may be spread 4 or 5 dm. in a year, but it 
probably takes several years to produce, on such an added area, a dense stand, 
such as was mentioned above, of 300 to 600 stalks to the square meter. Another 
means of spreading to more distant parts of the harbor is through transporta- 
tion of whole tufts or mats of rhizomes by the ice. The stubble, which is tough 
in early winter, may apparently be frozen in blocks of ice at low tide, and when 
these blocks float up with the rising tide whole clumps of Spartina, with 2 or 3 
dm. thickness of mud tangled among its rhizomes, may be lifted and carried to 
other parts of the harbor. It is only when these clumps happen to be dropped 
on bottom at or above the 1.5-foot level that they persist for more than one 
season. It might be assumed that clumps lodging below the 1.5-foot level dis- 
appear in winter through the agency of ice, but, as a matter of fact, they do not 
thrive even for one growing season. Dead clumps of turf are often seen on the 
bottom, showing where living turfs have been dropped. Harly each summer 
one or more considerable clumps of the grass are found growing in new loca- 
tions, sometimes near the very middle of the harbor. The death of this grass at 
levels below 1 foot or even 1.5 feet is probably due to its inability to withstand so 
long a submergence as it is there subjected to. Experimental work is under way 
by which we hope to determine whether this is the real explanation. 
A very interesting feature of the distribution of 9. glabra at its lower limit is 
the suddenness with which it ceases to spread downward over the bottom when 
the 1.5-foot level is reached (plate 1114). The soil may be quite densely covered 
with Spartina even at the lower limit of its distribution, and the presence of its 
rhizomes gives the bottom sufficient firmness to enable it to support the weight 
of a person walking over it. The bottom just beyond that bearing Spartina 
drops abruptly to a level 6 or 8 inches lower. This lower bottom is usually very 
soft for a depth of several decimeters. About tide-pools and the little inlets 
making into the mid-littoral marsh, near 2,500 north by 200 east, we find this 
same sudden drop to lower and softer bottom. It is difficult to see why the 

* Once only (at 100 north by 1,000 east) were seedlings of S. glabra found growing 
in the peaty mud among the parent plants near the 6-foot level. 
