40 BOTANICAL GAZETTE [JULY 
In stems this proliferation of cells became first evident at thelenticels 
by their increase in size and the protruding of white tissue, as shown 
in the lower portion of the stem in fig. 7. RICHTER (12) has noted 
a similar proliferation of tissue at the lenticels of Vicia villosa under 
the influence of tobacco smoke. STONE’s similar results have 
been cited. In the roots this tissue was abundantly developed 
in some cases, particularly in Hibiscus, which is shown in fig. 7, 
where B and C are plants which were subjected to a slow stream 
of illuminating gas for a period of 30 days. Fig. 8 shows detailed 
structure of these proliferations in the roots of Hibiscus. The cork 
Fic. 7.—Hibiscus: A, control; B, C, treated with illuminating gas 
layer of the abnormal root has been sloughed off. Practically the 
same morphological situation appears in this case as in Adlanthus 
previously figured. 
A similar response by lilac is shown by drawings of fig.9. These 
abnormalities were recorded for Hibiscus, lilac, Croton, Diervilla, 
Ricinus, Ulmus, and pear. 
An experiment similar to the foregoing was carried out with an 
Ailanthus growing on the campus near the Hull Botanical Labora- 
tory. The tree had a diameter of about 8 cm. and a height of 3.5 m. 
Ata short distance were other trees of the same species which served 
as controls. Illuminating gas was admitted to the roots of the 
