134 THE RELATION OF PLANTS TO TIDE-LEVELS 
monthly emergence from 736.5, the average total number of hours in each 
month. The emergence for the higher levels was obtained by subtracting the 
monthly submergence from the average number of hours in a month. The 
exposure of any level varies greatly, of course, from month to month. Thus, 
e. g., the —1-foot level was not exposed at all in August 1911, while its probable 
emergence for May was 9.5 hours. Again, the probable submergence of the 8.75- 
foot level for August 1911 was 0.0 hours, while for May it was 11.25 hours. 
The average monthly emergence of levels between mean low water and 3 feet 
was obtained by measurement on the predicted tide-curve for Willet’s Point for 
August, since the mean low water for this month (0.038 foot) was closest to that 
for the whole six months of the growing season (0.006 foot). The submergence 
of levels between 4 feet and 6.5 feet was obtained by measurement on the 
predicted curve for June 1911, since the average high water for this month was 
exactly that for the season (7.63 feet). 
The fourth and fifth columns of Table A show respectively the average 
emergence and submergence per lunar day of 24.88 hours, there being 29.6 lunar 
days per month, or 177.5 lunar days per growing-season. From these data, or 
those for the month, the total emergence or submergence for each of the 59 tides 
per month (average) or 355 tides per season can be obtained. 
The sixth column of Table A gives the ratio of emergence to submergence for 
each level. These figures will be of value when discussing the upper and lower 
limits of plant distribution (see Section VI), since from them we can see the 
proportion of submergence to emergence endured by any plant at its upper or 
at its lower limit. 
Another series of tidal data of interest in connection with plant distribution 
is that concerning the frequency of submergence or emergence respectively of 
levels near the upper margin and the lower margin of the littoral region. From 
- the predicted heights of the low waters and of the high waters for each tide of 
the season, given in the United States Tide Tables for Cold Spring Harbor, it is 
possible to determine exactly the number of tides each month, or the total num- 
ber per season, in which any level near high-water mark will probably be 
submerged, or any level near low-water mark will probably be exposed, the only 
uncertainty in these cases being the possible effect of the wind in making the 
level attained higher or lower than that predicted. 
Table B (p. 186) shows the number of submergences per month and per 
season (May to October) of levels from 6 to 9 feet. These numbers were 
obtained directly from the Tide Tables by adding the 0.4-foot correction to the 
predicted high waters for Willet’s Point for each tide of the growing season. In 
connection with these numbers it should be recalled that there are 355 tides per 
season, which includes 58 each for June and September, 59 for October, and 60 
each for May, July, and August. From this table of infrequent submergences 
can be deduced the duration of the longer continuous emergences of these high | 
levels. 
Table C (p. 186) shows the number of emergences per month and per season 
of levels between —1.25 feet and +1.75 feet. These figures, like those in Table 
B, are taken from the heights of predicted low waters for Willet’s Point, which 
are in this case identical with those for Cold Spring Harbor. From the 
