376 PEIRCE: FoRCIBLE DISCHARGE OF 
at some of the slides, but it was too late to examine all and the 
light was uncertain at best. Slide no. 1 had some dead anthero- 
zoids sticking to it. I did not see any on the other five slides exam- 
ined, I put no. 1 back and brought the other five with me for 
more careful examination in the laboratory. The day had been 
warm and sunny, the air was much dryer during the day than at 
night, and there was some breeze throughout the day (a circum- 
stance which might account for there being no antherozoids on any 
slides except no. 1). By seven o’clock in the evening it had begun 
to rain, and it rained gently for three hours. 
There was white frost on the lowlands on the morning of Janu- 
ary 21, but none on my bank. At g.30 I took a microscope out 
again. Slide no. 1 had water on it, making a ridge along the 
lower edge on the side next the bank. I carefully took the slide 
out of the wire holder, turned it flat so that the water spread over 
the upper surface, and put it on the microscope. There were 
Asterella antherozoids in considerable numbers—a dozen in one 
field of Leitz objective VI and ocular 3—swimming about in the 
water. These antherozoids could have come upon the slide only 
as did those dead ones found on it the afternoon before, by being 
forcibly projected from the antheridia imbedded in the plants. It 
is evident, then, that the antherozoids are expelled when the plant 
is under perfectly natural conditions, and that what I saw a yea? 
ago was not a laboratory phenomenon merely. . 
From the conditions prevailing when I first saw the expulsion 
of these antherozoids, I thought the mechanics of the process 
might be as follows: that the walls of the antheridia and the 
adjacent tissues of the plant give up water in comparatively dry 
air faster than the contents of the antheridium can; that pressure 
develops which finally exceeds the resistance of the wall of the 
antheridium ; that this breaks suddenly and the antherozoids ar© 
thus thrown out through the openings of the cavities in which the 
antheridia lie. This hypothesis seemed to be strengthened by ™Y 
finding antherozoids in the afternoon, after a day of comparative 
dryness following a night when the dew was heavy. But the 
occurrence of antherozoids on the slide which was out all night 
and during a rain does not favor this view. The number of 
antherozoids on this was decidedly larger, perhaps because 
