1916] COSENS & SINCLAIR—AERIFEROUS TISSUE 225 
Fic. 11.—Salix purpurea L.: section across the male reproductive axis 
when the catkin is just. emerging from the bud; aeriferous tissue is clearly 
differentiated in the pith; X 7o. 
Fic. 12.—Same as preceding except that the catkin was sectioned at a later 
stage; aeriferous tissue has opened out, making more apparent the air spaces 
and sa separating strands of cells; X7o. 
13.—Salix humilis Marsh.: showing aeriferous tissue developed in the 
pith is he male reproductive axis; X70. 
Fic. 14.—Salix cordata Muhl.: aeriferous tissue in the pith of the male 
ica e axis; a comparison with fig. 2 shows similarity of this tissue with 
that incited by gall stimulus in the stem pith of this species of Salix; X70. 
