418 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1931 



ering the surface of water. In ponds about Ithaca where these 

 species grow in abundance few larvae are present. However, our 

 knowledge of the growth or culture of these plants is very limited. 

 A pond (pi. 4, fig. 2) which for years past had a compact covering of 

 Leinna minor suddenly in 1929 became densely coated with Wollfla' 

 punctata^ the Lemma occurring onl}'' in small patches. 



From all these conflicting observations one fact stands out clearly — 

 that the study of the growth, culture, distribution, and usefulness of 

 surface-loving plants deserves the especial attention of botanists and 

 those engaged in the problems of mosquito control. This may be 

 further emphasized by the report of Williamson (1928) that in 

 Malaya the blue-green alga, Microcystis^ forms a dense scum in foul 

 waters, and this accounts for the absence of anopheline larvae. 



NONSURFACE-LOVING AQUATIC PLANTS 



Though predacious and surface-loving aquatic plants deserve more 

 study, those graceful plants belonging to the Characeae aroused the 

 attention of mosquito workers when Cabellero (1919) announced 

 that Chara foetida had a marked effect in inhibiting the develop- 

 ment of mosquito larvae. This and his later studies awakened a 

 renewed interest in the study of aquatic vegetation in relation to 

 mosquito breeding. These studies have centered largely about the 

 Characeae^ and numerous conflicting reports have been published in 

 recent years. The various species of Chcvraceae (pi. 7, fig. 1) are 

 beautiful and graceful plants often growing with remarkable vigor 

 and forming a most pleasing bottom covering for otherwise un- 

 sightly ponds. The species of Characeae are very difficult to identify, 

 and many workers seem to be of the opinion that certain species do 

 inhibit larval growth, while others have no effect. What are these 

 species? This question has not yet been answered, for the experi- 

 mental work with the various species has been very limited. Most 

 of the published results deal with general field observations, and 

 there is no indication by these various authors as to the exact con- 

 ditions under which the observations were made. Was the Chara 

 sp. growing vigorously? Were the ponds fouled with wastes? 

 Were they temporary or permanent ponds? Were they spring fed, 

 from overflows, surface water, or from other sources? In other 

 words, an exact analysis of the aquatic environment is seldom given. 

 In general, such workers as Allaud (1922) in Morocco, Langeron 

 (1921) in Tunis, Maynar (1923) and Pardo (1923) in Spain, Federici 

 (1928) in Italy, and Buhot (1927) in Australia have presented brief 

 experimental data that seem to confirm the findings of Cabellero. 

 On the other hand, the work of MacGregor (1924) in England, 



