INTRODUCTION 
13 
known are those induced by Exoascus turgidus on the Birch, 
and by Peridermium elatinum on Silver First (Plate XVII.). 
Galls on Algae, Mosses, and Lichens 
A. W. Bennett has described a gall occurring on the alga 
Vaucheria Dillwyni Agardh., probably caused by the rotifer 
Notommata Wernecki Ehrenb. Similar galls on various 
species of Vaucheria have been recorded by Continental 
observers. This gall is of very variable size and aspect, 
often assuming the form of an elongated capsule bearing 
numerous prolongations or tubercles on its surface ; the 
causer may be discerned, with the aid of a lens, within 
the gall, appearing as a little black point. A copepod 
(Harpacticus chelifev O. F. Muller, according to Barton) 
galls Rhodymenia palmata, causing numerous papules on the 
thallus. A similar agent deforms the thallus of Desmarestia 
aculeata Lamouroux. 
Connold depicted (“ Plant Galls,” Fig. 278) stems of 
Halidrys siliqua Lyn. with pronounced globular swellings. 
They were picked upon the beach at St. Leonards in 1902, 
between November and April, after heavy storms. “ Many 
efforts were made to determine the cause, but without 
success.” 
Eelworms cause galls on algae and on mosses ; for notes 
concerning these, see Chapter VIII. There is a reference 
in Chapter VII. to galls on lichens supposed to have been 
caused by mites. 
The majority of the agents causing galls on British 
Phanerogams and vascular Cryptogams are insects included 
in the orders Hymenoptera , Coleoptera , Lepidoptera , Diptera , 
and Homoptera. These and the galls caused by Mites 
(Acari ), Eelworms ( Nematoda , family Anguillulidae), and 
Fungi are discussed in the following chapters. For the 
most part, familiar galls only are described, the text being 
chiefly descriptive of the plates. 
