INSECTS AND FLOWERS. 
117 
Viola , known as Melanium , has a very remarkable form of 
pollen-grain. They are of a (comparatively) enormous size, the 
lateral aspect presenting nearly a rectangular parallelogram, the 
transverse aspect a nearly regular pentagon or hexagon. Fig. 40 
represents the two views of the garden pansy, fig. 41 the side view 
of Viola lutea , and fig. 42 the transverse view of V. cornuta , 
offering a remarkable contrast to the size and form of the grains 
in the section Nominium of the same genus (see fig. 13). There 
is no doubt that this variation is connected with a difference 
in the mode of fertilisation in the two sections — a view which 
is confirmed by the great difference in the form of the stigma. 
The form of pollen-grain covered with a number of distinct 
sharp spines, is characteristic of certain natural families, especi- 
ally Malvaceae, some sections of Composite, and some Cu- 
curbitaceae. They are usually, but not always, spherical. 
Fig. 43 is the very large and beautiful grain of the hollyhock 
{. Althcea rosea). The grain of the garden Cineraria (fig. 44), 
presents about twenty-four of these spines round any diameter. 
Fig. 45 is the spherical grain of the dandelion ( Taraxacum 
officinale ) ; fig. 46 the ellipsoidal furrowed one of the groundsel 
(Senecio vulgaris). 
Pollen-grains fastened together by viscid threads, so as to 
enable them to be carried about with greater facility in masses, 
are of various sizes and forms. One very familiar variety 
occurs in the various species -of Rhododendron and Azalea ; 
another is afforded by the well-known triangular grains of the 
Onagrariese, as illustrated by the Fuchsia (fig. 47 ), and another 
by the “ touch-me-not,” or Impatiens. The same occurs in 
Oaryophyllacese, as Stellctria Holostea (fig. 48), and Lychnis 
cliurna (fig. 49), where the grains are also covered with a 
great number of tooth-like or wart-like projections. The 
smooth oval furrowless grains of Salix nitens (fig. 50) are 
connected together in the same way. A different mode of 
adhesion is exhibited by the pollen of Canna inclica (fig. 51). 
The grains are first of all hexagonal, and firmly attached 
together by their sides ; but after they become separated from 
one another appear almost perfectly spherical ; they are 
furnished with a number of minute spines. A very similar 
appearance is presented by the pollen of Alpinia (fig. 52). In 
the cultivated “white Arum” Richardia africana (fig. 53), the 
grains are variable in size, oval, without furrows, and connected 
together in long strings and masses. The pollen-grain of 
Cobcea scandens (fig. 54), is one of the most magnificent 
objects under the microscope. Perfectly spherical in outline, 
and nearly of an inch in diameter, its surface is cut up into 
minute hexagonal facets, reminding one of the eyes of a fly. 
A very interesting illustration of the relation between the 
