AERIFEROUS TISSUE IN WILLOW GALLS 
A. CosENS AND T. A. SINCLAIR 
(WITH PLATES II-IV AND FIVE FIGURES) 
CosENs (2) has demonstrated recently that in certain willow 
galls there is a production of aeriferous tissue in regions where it 
is not present normally. This investigation has been undertaken — 
for the purpose of explaining the unexpected appearance of this 
tissue. Many different species of Salix and Populus were examined 
in order to determine the normal distribution of the tissue in their 
various organs.. As an important adjunct of the work experiments 
have been conducted for the purpose of observing the influence of 
certain factors on its production, such, for eeAp le, as tempera- 
ture, water, nutrient solutions, and light 
Stated in general, intercellular spaces are found in the paren- 
chymatous tissues of nearly all plants. These usually remain small 
and inconspicuous, although connected with one another in such 
a way as to form a continuous gas-containing system of cavities. 
In many plants, however, especially hydrophytes, these spaces are 
so large and conspicuous and formed on such a regular plan as to 
impart the well known characteristic appearance to the areas in 
which they occur. Such a typical tissue is designated here aerifer- 
ous tissue. 
Concerning the occurrence of this tissue in certain histological 
regions of Salix when under abnormal stimulation, two explana- 
tions present themselves: (1) that the tissue is an “environmental” 
modification, produced by the action of the plant protoplasm in 
direct response to certain conditions of the environment; (2) that 
the tissue is a distinct type, probably of wider distribution in the 
ancestral forms of the group, but now absent in certain regions of 
the modern species, since the power to produce it is dormant, but 
reinstated when these tissues are subjected to suitable stimulation. 
One example will suffice to illustrate the line along which attention 
has been directed. In many aquatic plants there are two types of 
leaves; for example, in Proserpinaca palustris L. the leaves on the 
Botanical Gazette, vol. 62] [210 
