mK 
24 MISSOURI BOTANICAL GARDEN. 
doubt, is derived from the fact that in this stage the plants 
were found to sink to the bottom of ponds and there pass 
the winter, and the following spring to rise to the sur- 
face again and begin anew the cycle of life. Biscoe* also 
made a careful study of this stage with like conclusions. 
This my study of the species proves true, but not the whole 
truth. I find that in midsummer if a pond gradually 
disappears through evaporation these ‘‘ winter fronds ”’ 
are produced in abundance, and as the shore line recedes 
they are found for a considerable distance up the bank, 
still in an apparently healthy state. To my knowledge 
ponds have entirely dried away and remained so during the 
winter, yet when the spring rains again renewed them the 
Spirodela reappeared, the first fronds emerging from these 
‘winter buds.’’ Hence they are a protection as well 
against drought as lower temperature. Hegelmaier ¢ also 
described a form of Lemna gibba in which the fronds are 
flat and three-nerved, much resembling LZ. minor. Guppy,t 
from a long series of observations and study,found that 
these < flat fronds ’’ performed the same functions as the 
‘winter fronds ’’ of 8. polyrrhiza, sinking to the bottom 
of ponds in the fall and rising to the surface again in the 
spring, then continuing active vegetative reproduction. In 
the middle of June, 1897, I discovered a pond in St. Louis 
abundantly covered with sterile ZL. minor. The first part 
of September I again visited it hoping to secure fruiting 
specimens. The water had almost entirely disappeared by 
evaporation and only a small number of normal plants re- 
mained. These were sterile, but I discovered that they were 
producing a modified frond similar to the ‘* winter frond ”’ 
of S. polyrrhiza. Further search revealed these modified 
fronds in abundance in the remaining water, in the oozy 
* Biscoe, T. D. The winter state of our Duckweeds. Am. Nat. 
7: 257-268. pl. 3. May 1878. 
+ Hegelmaier, Friedr. Monogr. Lemnac. 146. May 1868, 
¢t Guppy, H. B. Habits of Lemna minor, L. gibba and L. polyrrhiza. 
Journ. Linn. Soc., Bot. 80: 325, 6 Oct. 1894. 
4 
