44O ENTOMOLOGICAL NEWS [Dec., 'lO 



experimenters had made any attempt to discover under what 

 conditions Azolla flourished naturally and, ecologically, the 

 plant was no better known at Hamburg than it was in New 

 Jersey. 



My next headquarters were at Amsterdam and my first real 

 acquaintance with Azolla was made at Boskoop, accompanied 

 by Dr. Quanije of the Phytopathological Service, Mr. 

 Moerlands of the Horticultural School and Mr. Ouwerkerk 

 of the Nurserymen's Association. Here, undoubtedly Azolla 

 -formed a complete vegetable carpet over every ditch and canal, 

 and mosquito breeding was practically impossible. So luxuri- 

 ant was the plant that it could be twice removed from the sur- 

 face during the season always leaving enough to restore the 

 covering promptly. 



During the next two weeks I covered the bulk of the "polder" 

 area in Holland, and found just where and how Azolla flour- 

 ishes. 



First of all, it occurs nowhere, so far as I could learn, out- 

 side of the "polders" or reclaimed areas, where the water was 

 all stagnant. Second, its point of greatest abundance coincides 

 with the most completely developed peat or turf area. Haar- 

 lem. Leiden, Boskoop and vicinity have every ditch and almost 

 every canal covered by an almost perfect carpet and these are 

 the richest peat areas in the country. South of Rotterdam where 

 there is a sand or clay addition, Azolla works out. and the 

 same is true east of Amsterdam, not a trace of it being seen 

 at Naarden. 



Nor does the plant maintain itself in shallow water, where 

 ice forms to the bottom. It comes in year after year only in 

 ditches three feet deep which never freeze to the bottom, and 

 where ground ice never forms. A severe winter is always 

 followed by scanty crop of Azolla next summer. 



In Belgium I did not see the plant at all ; but I had neither 

 the time nor the funds to continue my investigations in that 

 country as I had done in Holland. 



As the practical outcome of my work I feel no hesitation 



