1913] KNIGHT & CROCKER—TOXICITY OF SMOKE 347 
Tradescantia guianensis, Selaginella Martensii, Tolmiaea Menziesii, 
Eupatorium adenophorum, and various echeverias are not inter- 
fered with at all by low concentrations of smoke in the air, and only 
slightly inhibited in their growth by great concentrations. The 
mature plants that are sensitive to tobacco smoke manifest it in 
three ways: (1) by chemotactic movements of the leaves; the leaves 
of Boehmeria utilis and Splitgerbera biloba showed epinastic move- 
ments when in a glass chamber of 4.5~-7 liters with 1-3 whiffs of 
cigar or cigarette smoke; in Boehmeria the movement continues 
beyond the vertical position, with the formation of spirals in 
the petiole; (2) by lenticular protuberances; the development of 
lenticular protuberances occurred in sprouts of the potato and 
stems of Boehmeria polystachya and Goldfussia glomerata in the 
presence of tobacco smoke; while in Salix rubra and Sambucus 
nigra such protuberances develop in moist air, the process is greatly 
hastened by tobacco smoke; guttation commonly occurs in this 
lenticular tissue, due, as Moxiscu assumes, to high osmotic pres- 
sure; (3) by fall of leaves; tobacco smoke causes leaf fall in many 
plants; this is especially true of leguminous forms; 24-48 hours 
of exposure to tobacco smoke causes almost complete loss of leaves 
in Mimosa pudica, Caragana arborescens, Robinia pseudacacia, 
Halimodendron argenteum, and others; paper and wood smoke 
were likewise very effective in producing leaf fall, and nicotine very 
weakly so. Moxtscu states that in the mature plants he was not 
able to determine the constituent of tobacco smoke that does the 
injury. 
IV. Observation and experimentation 
AN OBSERVATION 
A mishap in the greenhouses of this laboratory has some of the 
virtues of a real experiment. An attempt to kill the insects by 
the common method of burning tobacco stems resulted in the acute 
poisoning of many of the plants. This application of a high concen- 
tration of smoke for a short time did not, of course, show responses 
in the nature of nasties, swellings, abscissions, and nulled tropisms, 
as observed by Mottscu with the application of lower concentrations 
