1915] 



HARVEY &■ ROSE— ILLUMINATING GAS 



37 



is brought about through an increase in size of the cortical cells, 

 and particularly by rapid proliferation at the phellogen layer. 



(/) Ailiiulluis seedlings; 

 illuminating gas; exposure 

 period 15 days; concen- 

 trations 1 :40c 1 : 10, and 

 controls. 



1 : 400 gave slight swell- 

 ing in tap root near the 

 surface of the soil; while 

 in the 1:10 the leaves 

 began falling after 5 days, 

 and had all fallen before 

 the end of the exposure. 

 The tap roots were much 

 swollen for 3-4 cm. below 

 the surface of the soil. 



e) Same as (</) but with 

 ethylene instead of illumi- 

 nating gas; concentrations 

 1 : 10,000 and 1 : 250. 



Swollen zone of tap 

 root was somewhat more 

 pronounced in the 1 : 10,000 

 than in the 1 1400 illumi- 

 nating gas above. In the 

 1:250 all plants had lost 

 their leaves within S days, 

 and the tap roots were 

 much swollen. The mor- 

 phological nature of these 

 swellings may be seen in 

 figs, s and 6. In fig. 6 

 are two outlines of trans- 

 verse sections of the tap roots of Ailantlnts seedlings in the region 

 where swellings take place; A , the control plant; B, a treated plant. 

 Fig. s shows the detailed structures of the regions outlined in A 



FlG. 3. — Catalpa seedlings: A, controls 

 treated with illuminating gas. 



