586 : ON THE USE OF POLLEN 
little triangular masses of a cellular structure, which are 
made darker by nitric acid. At a later period, these are con- 
nected together by a cellular growth, but are made suffi- 
ciently evident by gently tearing the pollen-mass in nitric 
acid. These compound pollen grains when ripe, are green, 
and formed of vesicles, some of which are transparent, others 
opaque. When these pollen grains are placed in dilute nitric 
acid, these vesicles, whose fovilla has now become opaque 
and coagulated, are seen to be separated by translucent lines 
of loosened membrane. From hence it will be perceived, 
that the pollen grains of Orchideous plants are always essen- 
tially of the same nature. 
The Junci have a compound pollen, consisting usually 
of three vesicles contained in a common membrane. The 
Ericinee, likewise, have a compound pollen, having in Erica 
and Arctostaphylos four vesicles arranged in a telzdbédeid 
figure; and in Rhododendron and Azalea three, on the 
same plane: these are not surrounded by a common mem- 
brane, but are furnished with threads projecting from their 
junctures, and very distinctly to be seen in the Rhodo- 
dendron. The nearly allied Epacridee have a similar 
pollen. 
The Onagrariacee have a highly remarkable and beautiful 
pollen, which can be most distinctly studied in Epilobium 
hirsutum; where the pollen grain appears to consist of three 
spindle-shaped vesicles united by filaments, and each burst- 
ing at both extremities, so that each grain has six points of 
dehiscence. In Fuchsia, it would appear as if these three 
vesicles were fused together so as to form a triangular mass 
with a single cavity and only three pores for bursting. It is 
worthy of notice, thatin Circeacee, there is the same kind of 
ollen. 
Although the compound nature of the pollen so well cor- 
responds with affinities, as we have seen, yet there are some 
important exceptions, as well as in the other characters we 
have studied. Thus, in /nga and Acacia amongst the Legu- 
minose, the pollen is compound: and Borago amongst the 
