CHAP. II. 
POLLEN. 
187 
in others it is covered with strong points, as Hibiscus syria- 
CLis ; in Jatropha panduraefolia it is granular ; in many 
Labiatae, banded; in Passiflora, reticulated; in Geranium syl- 
vaticum, crested ; in Armeria vulgaris, polygonal, with crested 
angles, among which are some of the most beautiful micro- 
scopical appearances in the vegetable kingdom. In all cases, 
where there are asperities of the surface or angles in the out- 
line, pollen is asserted by Guillemin to have a mucous sur- 
face, which was first observed in Proteaceae by Brown. But 
Mold finds that the presence of mucosity upon pollen is a 
constant character, at least when the grains first quit the 
anther ; and that a power of secreting a viscid substance is 
one of their functions when perfectly smooth, as well as when 
covered with points and inequalities. He, however, admits 
that hispid pollen is generally more viscid than that which is 
smooth. 
The figure of the granules is various ; most frequently it is 
spherical or slightly oblong. Many other forms have, how- 
ever, been described. The cylindrical exists in Anethum 
segetum, and in a very remarkable degree in Tradescantia 
virginica, where the grains become curved : in Colutea arbor- 
escens, they were observed by Guillemin to be nearly square ; 
in Lavatera acerifolia to be oval, much attenuated to each end ; 
in GEnothera they are triangular, with the angles so much 
dilated as to give the sides a curved form ; in Jacaranda 
tomentosa I have remarked them to be spherical, with three 
projecting ribs tapering to either apex ; in Cichoraceae the 
granules are spherical with facettes ; in Dipsaceae a depressed 
polyedron; in Scabiosa caucasica, patelliform and angular. 
In numerous plants it is oval, with a furrow on one side, like a 
grain of wheat; in Thunbergia fragrans, Mimulus moschatus, 
&c., it is strongly ribbed, as if formed of many folds ; in 
Morina persica, cylindrical, with a narrow neck rising ab- 
ruptly from each side ; in Scolymus, Scorzonera, &c., it is 
a polygon, with crested angles ; and of all these there are 
numerous modifications, some of which are represented in 
Plate IV. 
In consequence of the great diversity of forms observable 
in pollen, it has been supposed that it might be employed in 
