592 ON THE USE OF POLLEN 
Again, in another group of twelve families, agreeing in being 
polypetalous dicotyledons, with hilose radicles, albuminous 
seeds, and parietal placente, we find three with superior 
ovaries, distinguished principally by the number in the parts 
of the perianth, the Papaveracee, Fumariacee, and Violacee ; 
and among those with parietal ovaries, the Homalinee, Passi- 
floree and Malesherbiacee, separated by characters taken from 
the same organ. In the former instance, modifications of 
the sexual apparatus possess a high importance; in the 
latter, those of the floral envelopes. I might bring forward 
many other examples of the truth of this principle. 
I will therefore proceed to examine the nature of the 
pollen in some of the most remarkable groups, for the 
purpose of ascertaining those in which it is of taxonomic 
value. 
It being doubtful whether the pollen be present in Aco- 
tyledonous plants, I shall pass over this division of the 
vegetable kingdom without further remark. 
In the Grasses and Sedges, the pollen is spherical, and 
opens by a single pore. 
In Rushes, the pollen is spherical, consisting of three ve- 
sicles, contained in a common investing membrane. 
In Typhacee, the pollen is variable in form, and bursts 
by a narrow orifice, so that the fovilla is discharged in a cy- 
lindrical mass. 
Among the allies of the Lily, those monocotyledons that 
have perigynous exsertion, the same kind of pollen prevails, 
with the exception, as far as I know, of a single family (the 
Alismacee). The common form is an elliptical transparent 
pollen, marked with a dark central line when dry, which dis- 
appears with the escape of a bubble of air when placed in 
water, at which time it rapidly becomes spherical: it rup- 
tures by a slit or chink, and when this takes place under 
acid influence, the external membranes peel off, and the fo- 
villa remains more or less of the original form. Sometimes, 
this pollen is opaque, from the fovilla having been coagu- 
lated by acid, while still in the loculus of the anther. 
