218 BOTANICAL GAZETTE [SEPTEMBER 
so that much interest attaches to an examination of this region. 
It is at the node more than elsewhere in the stem that the aeriferous 
tissue is most abundant and characteristic in both willows and 
poplars. Thus in P. balsamifera it is particularly abundant imme- 
diately around the leaf traces, especially in close approximation to 
the bundle. The branch gaps likewise are occupied by this tissue, 
in the case of Salix extending well into the pith (fig. 8). In stem 
galls, for example, Phytophaga rigidae O.S. on Salix rostrata, this 
feature is always very pronounced; but most significant of all, the 
pith at the bases of the branches is typical aeriferous tissue. Fig. 9 
illustrates this feature clearly, and is interesting in comparison with 
fig. 10; both are from Salix lucida, the former from the base of a 
branch, the latter from an internode. 
Lear.—The petiole is sometimes a vestige carrier, so that it is 
of interest to note that aeriferous tissue has been located here in 
several species of Salix and Populus, for example, Populus bal- 
samifera, Salix humilis, S. fragilis, and S. cordata. As a rule it is 
confined to the part of the petiole adjacent to thestem. Elsewhere 
the ground tissue is of the compact type. In the blade there is no 
indication of it, as the palisade layer and spongy parenchyma are 
of the ordinary type. Yet in the leaf gall Pontania pomum on Salix 
cordata, practically all of the ground tissue is aeriferous. 
Seanuncs: —The seedlings of Salix serissima Fernald only were 
examined. These were obtained by sprouting the seeds in a moist 
chamber between layers of filter paper in an incubator, and then 
pricking the young seedlings into small fern pans. Different stages 
were examined, but in none was aeriferous tissue found in the pith. 
It is present in the cortex. 
Root.—The roots of the Salicaceae are devoid of a pith. The 
primary cortex, however, was examined in the roots of seedling 
plants of Salix serissima, and in young roots of Populus balsamifera 
and P. nigra, and was found to consist in part of a well differentiated 
aeriferous tissue. 
INFLORESCENCE.—No part of the plant is considered more 
important asa retainer of vestigial tissue than the reproductive 
axis. It is of especial interest to find, therefore, that aeriferous 
tissue is developed and often beautifully typical and abundant in 
