1382 THE RELATION OF PLANTS TO TIDE-LEVELS 
above) chiefly on the average or mean range of the tides from end to end of the 
growing season. For plants growing just below mean low water or just above 
mean high water it is probable that the occasional extremely. low tides or 
extremely high tides may be of great, possibly of preponderating or critical, im- 
portance (see p. 15 above). We shall look into this latter question in more 
detail later on. 
It is evident that the direct primary effect of this oscillation of the water- 
level, twice each “lunar day” of 24.9 hours, will be the twice repeated sub- 
mergence by the water and exposure to the air of all plants growing between 
tide-marks. While the roots and submerged portions of the shoot are under 
water they are wholly or partially shut off from the light and completely shut 
off from a supply of air, except as this may be conveyed to them from the exposed 
portions or absorbed from the submerging water. ‘The possible secondary effects 
of this submergence and exposure we shall attempt to analyze later on. 
The determination of the exact time of submergence and exposure of soils 
and plants at the various levels necessitates carefully made and recorded 
observations of the rate of rise and fall of the tide. Since no such data for the 
Inner Harbor at Cold Spring Harbor were available, measurements were made 
in the manner described on pages 12 to 14 above. These measurements are 
expressed in the curve shown in plate v1, which was briefly described earlier in 
this paper (p. 13), in order that the data embodied in it might be used in the 
discussions in Section III. 
The chart referred to gives the curve for two successive tides of a single lunar 
day. ‘The tides chosen are of about mean range. From this chart the sub- 
mergence and exposure, by an average tide, of all levels of the shore between 
mean low water and +-7 feet, might be determined. But in order that the aver- 
age submergence and exposure during the growing season of these levels, and of 
levels lower and higher than these, might be determined, records of all tides, 
‘from May to October, were needed. Since we were unable to make these by 
actual measurement at Cold Spring Harbor, recourse was had to the records of 
actual tides, and especially to the predicted tide curves, for Willet’s Point, New 
York. This is the nearest tide-recording station of the U.S. Coast and Geodetic 
Survey and is the “ standard port for reference ” for Cold Spring Harbor. An 
actual recorded curve for Willet’s Point for July 18, 1894, is shown in the chart 
in figure 4.° This shows the form of curve for a tide of mean range. This curve 
has the general form of that for the tide of mean range at Cold Spring Harbor, 
though it shows a slight flattening at the top, and a striking retardation in the 
rate of fall of the water-level just before mean low water is reached. Plate xx11I 
shows a portion of the “ predicted tide curve ” for May 1911, made by the tide- 
predicting machine of the Coast and Geodetic Survey. 
In these predicted curves for tides at Willet’s Point those for mean tides 
show a close resemblance to the curve of the actual mean tide at Cold Spring 
Harbor. We may, then, assume, what is highly probable, that the curves of 
actual tides of neap range and of spring range at Cold Spring Harbor would 
resemble in general those for the same tides at Willet’s Point, just as the curves 
*The writers are greatly indebted to Mr. O. H. Tittman, Superintendent of the 
Survey, for his kindness in having the curves of actual tides traced and in having 
the predicted curves, for the season from May 1 to October 31, 1911, made anew 
for us, by the new tide-predicting machine of the Survey. 
