Peirce . — Studies of Irritability in Plants. 451 
for nine months, is tiresome, and I shall in the future use one motive 
power for as many cultures as possible. Furthermore, no spring clock 
is absolutely reliable, and though these cheap clocks have served me well 
enough to enable me to reach certain results, they are not suitable for 
experiments lasting months at a time. I have lost many cultures because 
clocks have suddenly stopped which had carried them regularly for 
months. The loss of time from this cause is often very great. I am now 
working on a motor which I hope will be both efficient and reliable, and 
at the same time require less frequent winding. 
I began my experiments on Liverworts and Ferns by using small 
flower-pot saucers of soft porous red clay. These, when used in pairs (the 
upper saucer containing soil, the lower filled with water), have the great 
advantage of furnishing well-drained culture dishes. On the other hand, 
being opaque, they cast a shadow over a greater or less proportion of the 
surface of the culture. For this reason, I have now used for some time 
crystallizing dishes of thin white glass, about eight centimetres in diameter 
and three and a half centimetres deep, covered with the lids or bottoms of 
Petri dishes. These lids, not fitting tightly, permit fair ventilation, at the 
same time that they exclude dust and retain moisture. Dull black paper 
is finally glued over the tops of the lids, so that all light falls nearly or 
quite horizontally. 
The soil used came from the surface of the banks where the Liverworts 
and Ferns grew from which I collected the spores. The soil was air-dried, 
freed from pebbles, pulverized in a mortar, and filled into the dishes to the 
depth of about a centimetre. The soil was moistened from the start with 
boiled distilled water only, for I wished to avoid an accumulation of salts 
from our hard tap-water in these undrained dishes. I have not attempted 
to supply equal quantities of water to the cultures, though I have taken 
pains to give no excess, and to water fairly uniformly. When the 
antheridia and archegonia of Anthoceros and Gymnogr amine were ripe, 
I watered abundantly once or twice, and, a few days after, poured off 
the excess. Thus I ensured swimming room for the antherozoids, and 
presently the sporophytes of both began to appear. 
In experiments on Anthoceros two sets of cultures were used, on 
sterilized and on unsterilized soil, for both species of Anthoceros common here 
(A. fusiformis , Aust., and A. Pearsoni , M. A. Howe) contain colonies of 
Nostoc (sp. ?). I have elsewhere reported 1 , however, that Anthoceros 
appears to grow better, and in other respects perfectly normally, without 
Nostoc , and for this reason it is quite fair to use only sterilized soil. 
The dishes, containing the duly moistened soil and covered, were sterilized 
on three successive days in an Arnold steam sterilizer, the last steriliza- 
tion lasting several hours. Though subsequent fungous infections cannot 
1 Peirce, G. J., Anthoceros and its Nostoc colonies, Bot. Gazette, xlfi, July, 1906, 
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