588 ON THE USE OF POLLEN 
exine, which closely resemble organized openings, such as 
the wrinkles in the pollen of Cruciferous plants; the six- 
sided reticular spaces in Martynia and Catalpa ; the spiral 
bands in Thunbergia; bands crossing each other in Passi- 
flora, Se, And what renders the absence of organized open- 
ings in such plants more than suspicious, is that by this 
character he separates genera belonging to the same family ; 
thus, in the Acanthacee, he represents Thunbergia as desti- 
tute of organized openings, and Justicia, Ruellia and Eran- 
themum as furnished with them. Believing as I do, that 
the tubular appearance of the boyau is produced by the 
protrusion of the coagulated fovilla through a minute orifice, 
I am led to consider the formation of this thread.like pro- 
cess as sufficient evidence of porous opening. In casting my 
eye over the notes of 440 observations of different kinds of 
pollen, when dry, when placed in water, and when immersed 
in diluted acids, I only find 19 where I could not produce 
dehiscence, and of those instances, some were of species 
belonging to Salvia, Anchusa, Lolium, Rhododendron, Plan- 
tago, Reseda, Spirea and Achillea, and must have been ac- 
cidental, as I have on other occasions caused them to 
protrude boyauz. 
There are two remarkable varieties of porous dehiscence. 
In the Rosacee and Leguminose, there are three equi-dis- 
tant pores, while in Berberidee and Polemoniacee, the 
number of openings in the exine are very numerous. I 
quote the foregoing as examples of the most ordinary forms. 
When the pores are numerous, it frequently happens that 
the fovilla is expelled only at three points, which are then 
equi-distant. To ascertain the type under such circum- 
stances, it is necessary to examine a great number of pollen 
grains; and this is one of the advantages to be gained by 
the employment ofa low magnifying power; the figure of the 
pollen will also assist ; when it is spherical or broadly oval, it is 
almost always multiporous; whereas, when very narrow, almost 
linear, in its dry state it is usually furnished with three 
pores. Again, an opaque exine is generally perforated by 
