SUBMERGENCE AND EXPOSURE 185 
frequency of emergence of each level here given the duration of the longer 
submergences of these low levels can be obtained. 
From Tables B and C it is evident that the — 1-foot level and all below it may 
be continuously submerged for a month at a time, e. g., during August. Even 
the 0-foot level may, as can be seen from the Tide Tables, be submerged con- 
tinuously for from 4 days at a time, in May, to 7 days in June or August. On 
the other hand, the higher levels may be exposed continuously, never being wet 
by the tides, for many days together. Thus, e. g., in 1911, the 8-foot level was 
continuously exposed for 10 days in June, or even 12 days in July. Even the 
7.5-foot level may be exposed continuously for 4 days at a time, in June, or 
even 7 days, as from August 30 to September 6, 1911. For levels above 8 feet 
the duration of continuous exposure would evidently be markedly greater. These 
unusual tides which submerge the higher levels and expose the lower ones are 
grouped in two series each month, 1. e., at the two periods of spring tides. This 
fact is of great importance to the plants growing at these levels. It means that 
plants at the —1-foot level, e. g., may be constantly submerged for a month at a 
time and then, after three or four periods of exposure, of from half an hour to 
an hour per tide, they may again remain submerged for a fortnight or a month. 
So far as enduring submergence is concerned, this is probably equivalent for 
the plant to constant submergence. The plant is, however, obliged occasionally 
to withstand the exposure to sun and wind. In fact, even such a brief exposure 
may be of critical importance in limiting the upward extension of a delicate 
species. 
With so much of general discussion of the tidal changes themselves, we may 
now turn to take up their effect on plants. 
TABLE A.—Duration of submergence and exposure, from May 1 to October $1, 1911. 


1 Max, 5.5; min. 0.0. 
2 This means that this level is exposed only z}, 
as long as it is submerged. 
3 Max. 9.5; min, 5.0. 

4 Max. 34.50; min. 12.5. 
5 This means that this level is exposed 353 time 
as long as it is submerged. 
6 June. 
7 Season. 
- AON Sabo pear owe Average Average Ratio. 
Level. Average per cal-| Average per cal: eed Se ob ae Sale Emergence. 
endar month. | endar month. | P&* *U24 Gay. | per lunar day. Submergence. 
Feet Hours. Hours Hours. Hours. 
—1.25 1.66 1 734.84 0.06 24.82 1.66/734.84= 0.0023 2 
—1.00 3.70 3 732.80 0.12 24.76 Bat MponOE= OUD tL 
—0.50 23.50 4 713.00 0.79 24.09 23.0 /113.0 = .0816 
0.00 53.70 682.80 1.82 23 .06 ~53.7 /682.8 = .0788 
+0.50 112.75 623.75 3.80 21.08 112..75/624.0 = .1791 
+1.00 180.40 556.10 6.10 18.79 180.4 /556.0 = .38244 
1.50 239 .25 497 .25 8.08 16.80 239).2/497.2°=  .4807 
2.00 261.25 475 .25 8.83 15.95 261.2 /475.2 =  .65500 
3.00 338.75 397.75 11.07 13.81 338.7 /397.7 = .852 
4.00 397.50 339.00 6 13.43 11.45 397°5°/339.0 =" 1.172 
5.00 461.50 275.00 15.59 9.29 461.5 /275.0 = 1.674 
6.00 533 .62 202.88 18.03 6.85 533 .62/202.88= 2.625 
6.25 559.50 177.00 18.55 6.33 559.5. /177.0 = 93.161 
6.50 575.50 161.00 19.44 5.44 575.5 /161.0 = 3.574 
6.75 601.50 135.00 20.32 4.56 601.5 /185.0 = 4.455 
7.00 639.50 97.00 7A UB f 2.67 639.5 / 97.0 = 6.593 
7.50 689.30 47.20 23 .28 1.60 689.3 / 47.2 = 14.60 
8.00 706.14 80.367 23 .86 1.02 706.1 / 30.4 = 23.26 
8.25 719.70 16.83 24.31 57 719.7:-/ 16.88= 42.76 
8.50 727.80 8.70 24.59 .29 127-8: fe Sal == 8S..65 
8.75 731.86 4.64 24.78 -16 731.86/ 4.64=157 51 
9.00 734.42 2.08 24.81 .07 734.42/ 2.08=853.09 5 
