1. The smoke from tobacco cigars and cigarettes which has been thoroughly washed in 15 per cent H2SO4 and 40 per cent NaOH is very toxic to the etiolated epicotyl of the sweet pea. In the case of cigar smoke thus treated, 1000 parts per million of atmosphere give a triple response: reduction of rate of elongation, swelling, and diageotropism of the portion growing in the impurity; 5000 parts per million of atmosphere completely stop elongation and produce a swollen knob, while the epicotyl remains vertical; still higher concentrations kill the epicotyl before any form change occurs. 2. On the basis of dry weight burned, the washed smoke from cellulose paper cigarettes is even more toxic. The characters of the responses produced are identical with those produced by smoke from tobacco cigars and cigarettes. 3. When smoke from equal amounts of cellulose paper, smoked as a cigarette on one hand, and burned as an open sheet on the other, are compared, it is found that the former is 50 times as toxic as the lat...