62 BOTANICAL GAZETTE (JULY 
barely visible; (7) antheridia all empty, new crop showing 4 cells. The 
majority of plants collected on this day were in the fourth or fifth stage. 
The tendency toward periodicity in the production of sexual 
cells is probably a hereditary character. That periodicity is not a 
series of simple responses to successive stimuli is shown by the obser- 
vation of WixiiaMs that individuals removed from the influence 
of the tides continue to show the usual periodicity, and by Hoyt’s 
statement that individuals produced by vegetative multiplication 
F529 S054 2/8 |#15:6:7 8.9 WM I12 13 14 15 16 17:18:19 2 
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— INIT, ed IMENTS | 
Fic. 1.—Chart showing tidal relations at Naples from March 28 to April 27, 1908, 
with record of crops of Dictyota for the same period. oo tide records were furnished 
by the Italian government, through the kindness of Dr. R. Donrn, of the Zoological 
Station at Naples. The chart is to be compared with similar C. for Bangor, 
tide and the height of the water in relation to the mean low-water mark of spring 
tides. The curved lines show the development of the sexual crops (male) of Dictyota 
for the respective periods with their relations to the tides. The numbers opposite 
th cat th 2 eh gre £ h anth i 
erjdium 
# : 
r WiC WW 
and never subjected to the influence of the tides show approximately 
the same periodicity as those in their natural habitat. The former 
observation was confirmed by me at Naples, and goes to show that 
the habit of periodical reproduction is fairly well fixed. The habit, 
however, must have had its origin in response to external conditions, 
and it is a matter of considerable interest to ascertain, if possible, 
what factor or factors gave rise to the periodicity. The only sugges- 
tion made thus far is that of Wittams that the effective factor is 
the increased illumination during low water of spring tides, a view 
from which Hoyt dissents. 
Wiit1ms’ hypothesis seems inadequate to explain the periodicity 
at Naples. Dictyota flourishes there at a depth of many feet below 
