Apr,, 1921] 
MCNAIR — RHUS DIVERSILOBA 
189 
on that of R. Toxicodendron. The pollen sacs of R. diversiloba are composed 
of two coalesced sporangia, as is common in angiosperms. Their dehiscence 
occurs by a longitudinal slit, developed where the two coalesced sporangia 
join. According to Edgeworth (4), the pollen of the Anacardiaceae is oval 
with 3 slits. The fresh pollen grains of Rhtis diversiloba are ellipsoidal, 
about 1/800 sq. mm. in horizontal area, with a width 1/3 to 1/2 the length. 
The exine is roughened by minute, sharply pointed projections. When 
the pollen grains are immersed in N/4 KOH they assume a spherical form 
with no color change. In the material treated (which had been fixed in 
alcohol and xylol, stained, and mounted in balsam like the rest of the plant 
material), the spores assumed spherical shapes or in some instances became 
rounded tetrahedrons. As is common in entomophilous plants, the pollen 
has no surfaces so modified as to permit the wind to take hold of it, of the 
nature of the bladder-like appendages of the pine pollen, etc. Whereas 
anemophilous pollen has a dry outer covering to prevent large masses of 
pollen from adhering to the flower and hindering wind transportation, the 
entomophilous pollen of Rhus diversiloba is surrounded with a sticky sub- 
stance so as to adhere to the feet and other parts of the insect. In common 
with other entomophilous flowers, R. diversiloba has perfume-secreting 
glands heretofore described which may serve to attract insects. The 
pollen itself being non-toxic and not wind-blown, the aerial transmission 
of the poison by the agency of pollen is quite out of the question. 
As in the female flower the stamens develop to a certain advanced stage, 
so the ovary develops in the male flower to the extent that an almost fully 
developed ovule is produced. Such development of an ovule in a flower 
which is functionally purely staminate, borne on a purely male plant, is a 
phenomenon which has been but rarely observed. Each ovary contains 
regularly but one ovule. The funiculus becomes curved at its apex, so 
that the body of the ovule lies against it, and, although the axis of the 
body is straight, the micropyle is directed towards the surface of origin; 
thus the funiculus appears as a ridge along one side of the body of the ovule, 
and the ovule is anatropous and consequently of the form most common 
among angiosperms. 
The ovule, in the mature female flower, fills the ovarian cavity. The 
outer integument, therefore, occupies considerable space. The micropyle 
is somewhat widely removed from the upper arching of the nucellus. The 
inner integument is widely tubular and lengthened outwardly over the 
nucellus, in which the embryo sac is again somewhat pressed back toward the 
inside so that a wider path is prepared for the pollen tube. The advantage 
. of an anatropous ovule is apparent when it is remembered that the pollen, 
tube advances along the wall of the ovary, and that the micropyle is thus 
brought near the wall. It is not surprising, then, that this plant with its 
eflicient apparatus for fertilization should have large fruit production. 
Numerous germinating pollen grains are found on the stigmas of open 
