1918] McNAIR—SECRETORY CANALS 271 
later. This process of crystallization probably has its cause in the 
evaporation of the menstrum. If these crystals be viewed through 
a petrographic microscope, they are seen to be birefringent, similar 
perhaps to those noticed by WIESNER (8) in the sap of R. vernicifera. 
On adding water the light colored globules disappear, but the 
brown ones remain. The addition of alcohol, on the other hand, 
causes the solution of the brown globules. 
The freshly exuded resinous sap of R. diversiloba has been shown 
to be the only part of the plant capable of producing dermatitis (2). 
Consequently those portions of the plant that do not contain the 
resin ducts do not have this kind of toxic effect. The non-toxic 
portions are the anthers, pollen, xylem, trichomes, epidermis, and 
cork cells. The poison has also been shown to be non-volatile, 
although it may be carried by the particles of soot in smoke. 
Inui (1) has noticed that the amount of secretion of R. verni- 
cifera is influenced by the conditions of light and atmospheric 
humidity. In potted plants the secretion lessened when carbon 
assimilation was hindered. Similarly secretion was. greater in 
damp than in dry air. This secretion therefore seems to bear a 
relation to transpiration and hence to turgor. As the degree of 
turgor varies indirectly with the amount of transpiration, other 
things being equal, secretion would be least when transpiration is 
greatest. Turgor, too, is a necessary accompaniment of growth; 
flaccid tissues do not grow larger. If those influences which affect 
R. vernicifera have a similar action on R. diversiloba, then secretion, 
and consequently the plant conditions for poisoning, would be 
greatest during that time of the year when the growth of the plant 
is most active and the tissues least resistant, in the spring. Obvi- 
ously enough, when the plant is in full leaf and when growth has 
iminished, its resistance to injury will be greater and its liability 
of poisoning less. 
In autumn the charming appearance of the luxuriant foliage, 
when it turns to many shades of scarlet and bronze, speaks a 
flagrant warning to its victims and is only especially alluring to the 
unsuspecting. Nevertheless, either the amount or the virulence 
of the poison in the autumn leaves is less than that of the normal 
mature leaves (3). Of the autumnal leaves the red are less toxic 
than the yellow, and when the leaves have finally withered and 
