1916] COSENS & SINCLAIR—AERIFEROUS TISSUE 213 
studied by the senior author; in this paper that of aeriferous tissue 
only is dealt with in detail. 
Distribution of aeriferous tissue in galls 
Aeriferous tissue is abnormally present in galls produced by cer- 
tain species of at least two distinct orders of insects. Thus it has 
2 
2.—Fig. 1, Gall of Rhabdophage triticoides Walsh on Salix cordata Muhl.; 
fig. 2, ews produced Rhabdophaga triticoides Walsh. 
been located in the dipterous galls Rhabdophaga triticoides Walsh 
and R. strobiloides Walsh, stem galls on Salix cordata Muhl., and 
Phytophaga rigidae O.S. on the stem of Salix discolor Muhl. It 
also occurs in the hymenopterous gall Pontania pomum Walsh, a 
leaf gall on Salix cordata Muhl. 
The stem gall Rhabdophaga triticoides Walsh is usually terminal 
or nearly so (text fig. 1), but sometimes occurs at varying distances 
