AN ENCYCLOPADIA 
OF HORTICULTURE. 
Pollen—continued. 
beyond genera; nor does similarity of form of grain 
necessarily indicate affinity. Zostera possesses one of 
the most curious forms, the grains in this plant being 
long, and extremely slender and thread-like. The colour, 
in most’ plants, is some shade of yellow, but in some it 
is deep orange (Lilium tigrinum), or red (Verbascum), 
or blue (Scilla), or deep purple, approaching black. 7 
The contents of the grain are known as the fovilla. 
They consist of viscid protoplasm, full of small starch 
granules and oil-drops. Amidst this mass, in general, 
lie two bodies, like nuclei, the nature of which has been 
made clear, by the researches of Elfving and of Stras- 
burger, within the past few years, and is most easily 
understood if we look to the Pollen of Coniferæ. In the 
„Scotch Fir, the very light Pollen has the outer coat 
prolonged into two outgrowths containing air, which 
render the grain light. ‘There is comparatively little 
difficulty in making out that there are three cells con- 
tained within the large cell seen in the middle, and the 
multicellular nature of the grain remains evident through- 
out its existence in the Fir. | 
In other Coniferæ, e.g., the Yew, the Pollen is egg- 
shaped, and there is a small part cut off by a partition 
at the smaller end, rendering the grain two-celled; each 
cell has a nucleus. In Monocotyledons and Dicotyledons, 
the structure is less easily traced. In some (e.g., in 
Pollen grains of Orchids), a small part at one angle of 
the cell contents becomes separated from the rest, (though 
a cell wall does not form between), and is called the 
“vegetative cell.” It draws itself away from the side 
wall, and becomes imbedded in the contents: of the large 
cell. For a time, it remains different in form from the 
nucleus of the large cell, but ultimately it becomes 
quite like that nucleus, so that there seem to be two 
nuclei. The vegetative cell, in many Pollen grains, 
breaks up into two or more cells, and, in sdme (e.g., 
Scirpus palustris), the process becomes quite complex. 
When the Pollen tube is formed, the nucleus and the 
vegetative cell, or cells, pass into it, and have been 
traced into the end of it that passes down the micro- 
pyle and comes into contact with the helper cells (see 
Ovule). It is supposed that they perform some very 
important function in the formation of the embryo. 
The formation of the vegetative cells in the interior of 
the Pollen grains is generally regarded as representing 
the formation of the male prothallium in such Crypto- 
gams as Selaginella. See Prothallium. 
POLLICARIS. The — of the terminal joint 
of the thumb; lin. 
POLLICHIA. A synonym * Trichodesma (which 
see). 
POLLINATION. The dusting of the stigma of a 
flower with pollen grains, as distinguished from fertili- 
sation, or the action of the pollen upon the ovule, 
which. gives rise to the development of the seed con- 
taining an embryo. Pollination must. precede fertilisa- 
_tion. It is effected in very different ways in different 
flowers, and the agents by which it is effected are 
manifold. The more important of these are here indi- 
cated; but the account must be brief, though volumes 
have "been written upon the subject of Pollination. 
Full information of the present state of our know- 
ledge of the matter will be found in Dr. H. Miiller’s 
| contain nectar, or afford other attractions for insect 
Pollination— continued. 
Prof. Thompson, is included in Miiller’s work referred 
to above, and includes almost all published up to 1883, 
The method of Pollination varies with the structure 
of the flower. In those plants in which the pollen and 
the ovules of the same flower ripen simultaneously, 
the pollen may be transferred directly from the anthers 
to the stigma either by the parts lying in contact, or 
by their lying in such a position that the pollen falls 
from the anthers upon the stigma. In cleistogamous 
flowers, or those (e.g., in Sweet Violets, Wood Sorrel) 
which, in certain plants, are formed in summer and 
autumn, and never open, but yet are often more pro- 
ductive of seeds than the conspicuous flowers, the pollen, 
while in the anthers, pushes pollen tubes to the stigma, 
which is thus Pollinated. In by far the greater number 
of hermaphrodite flowers, even of those in which the 
pollen and the stigma mature simultaneously, the 
pollen is prevented from falling upon or reaching the 
stigma by the arrangement of, the parts. Necessarily, in 
those hermaphrodite flowers in which the pollen and 
the stigma do not mature simultaneously, the pollen 
cannot reach the stigma of the same flower (see Pro- 
and Proterogynous). In all these 
cases, the pollen must be transferred from the anthers 
to the stigmas by some agency from outside the 
flower; and this must be so yet more evidently in the 
case of unisexual flowers, whether male and female 
flowers be on the same plant or on different ones. The _ 
chief agents that effect Pollination in British plants 
are wind and insects. A few plants are adapted for 
conveyance of pollen by currents of water; and, in the 
tropics, humming-birds, and certain other birds, probably 
aid materially. ee ee ne 
latter agencies, since they would probably not a 
under notice in gardening operations nt all im the British 
Islands. Plants suited for fertilisation by wind are 
usually called “anemophilous,” or wind -lovers (from _ 
anemos, the wind, and phileo, I love). Those adapted — 
to have the stigmas Pollinated by insects, are called 
“entomophilous,” or insect-lovers (from entomon, an in- 
sect, and phileo, I love). They differ from one another 
so widely that a practised observer can conjecture almost 
with certainty to which group any flower would belong, 
though previously quite unacquainted with the flower. 
The more distinctive characters of the two are as 
follows : Anemophilous flowers are seldom large or 
conspicuous individually; the sepals and petals are 
small, usually regular, often absent, or reduced to one- 
row of small, scaly bodies (e.g., Oak); they seldom 
visitors; the stamens have long filaments, with versa- 
tile anthers, that turn with the least breath of wind, __ 
and thus shed readily the loose, powdery, smooth pollen, __ 
which is often produced in very great amount. = 
grains are very light, and are occasionally (e.g., in 
Firs) rendered relatively lighter by means of dilatations _ 
of the outer coat filled with air. The stigma in such 
plants is usually furnished at the end (Pellitory) or along — 
the sides (Grasses, &c.) with a quantity of long, simple 
or branched hairs, which frequently hang out beyond the 
perianth, or other coverings, e.g., beyond the glumes in 
pollen grains when these are 
ie Anemophilous plants 
a y trees under this group produce 
their flowers in spring, before the leaves, thus prevent- 
ing great loss of pollen among the leaves, and favouring 
Pollination. Entomophilous flowers are the reverse of all 
They are almost always more or less individually ` 
conspicuous, with well-developed, coloured petals, and — 
often also coloured sepals, or are crowded in show 
are sometimes —— but more 
