1918] McNAIR—SECRETORY CANALS 269 
reunited bundles placed under the endophloem; the other, the 
dorsal, has s—7 bundles arranged in an arc, and has also 5-7 resin 
passages in the phloem parts. 
All lateral ribs contain at least one passage on their dorsal sides, 
which is in the phloem as usual. Some of the resin canals seem to 
end blindly in the spongy parenchyma and palisade parenchyma, 
while others apparently anastomose in a reticulate manner like 
the vascular bundles which they accompany. 
TRECUL (7) noticed in Rhus Toxicodendron L., to which R. diver- 
siloba is very closely allied, the obstruction of the resin canals at 
the base of the petiole just before the fall of the leaves. This 
obstruction is effected by an increase in the parietal cells of the 
canals, and thus constitutes an instance of tylosis, similar perhaps 
to the obliteration of the old canals in the bark. The enlarged 
cells divide and the new ones produce more of the same kind. Soon 
the ducts are seen on the outside of the parenchyma at the place 
of insertion of the leaves. At a small distance away in the leaflet 
the passages have a normal appearance and are filled with sap. 
Resin passages in R. diversiloba are found also in the mesocarp 
of the fruit and in the hypocotyl and cotyledons of the embryo, 
likewise in the phloem. It is interesting to notice how early in the 
life of the plant these organs of secretion are found, and yet they 
are confined from first to last in the phloem group. 
According to Sreck (5), the resin canals of the Anacardiaceae 
are of schizolysigenous origin.t The first development of the inter- 
cellular cavities can readily be observed in R. diversiloba, which has 
good clear channels. In the beginning the evolution of the resin 
tube in this plant is clearly schizogenous. It forms itself from a 
little group of cells individually much narrower than the other 
parenchyma cells. A short slit soon appears toward the center 
of the group. When this slit enlarges itself, a little of the resinous 
Sap appears. The opening, first irregular in outline, enlarges to a 
channel of considerable size with a regular circular outline and is 
bordered by narrow cells. This is by far the form most commonly 
*It should be stated that Srecx worked with A nacardium occidentale, which is not 
very closely related to Rhus diversiloba, a fact which may explain the apparent differ- 
ence in origin of the secretory canals. 
