ESSENTIAL FLORAL LEAVES. 10g 
line. This condition is common among gymnosperms. A female 
flower of yew, for instance, consists of a single straight ovule 
terminating a short axis crowded with scale leaves. It is much 
rarer among angiosperms. The solitary ovules of docks and 
nettles are examples. Sometimes the nucellus, with its covering, 
is bent or canipylotropous, as in campion and shepherd’s purse. 
The commonest condition, however, is the inverted or anatropous 
one. Here the ovule turns sharply down on its stalk, part of 
which unites with the integuments, and forms a ridge or raphe. 
Cross-section of larkspur. lily, or hyacinth ovaries will show 
this well) The ovules of pinus, though without stalks, must be 
considered anatropous, since their micropyles are downwardly 
directed. 
It will be remembered that the flower was defined (p. 92) as a 
spore-producing organ, and we have seen that a pollen sac is a 
spore case or sporangium, producing numerous pollen grains or 
spores. An ovule is another kind of sporangium, which produces 
only one spore, called in this case an embryo sac, for reasons that 
will presently appear. One of the cells of the nucellus in a 
young ovule very early becomes larger than its neighbours. 
This is the embryo sac. It does not, like a pollen grain, become 
free, but is destined, if the conditions are favourable, to originate 
a rudimentary plant or embryo within it, which, surrounded by 
other structures developed from the ovule, will ultimately consti- 
tute the ripe seed. The embryo sac in the mature ovule of the 
angiosperm! (fig. 49) is no longer a simple cell; it occupies a 
considerable part of the nucellus, and its apex directly adjoins 
the micropyle. In its interior is an abundance of protoplasm, 
with large vacuoles, and a central nucleus, the embryo sac nucleus. 
Six small cells are also contained within the embryo sac, three 
at its apex and three at its base. The former are known as the 
egg apparatus, the latter (being exactly opposite) as the antipodal 
cells. Two of the cells composing the egg apparatus are smaller 
than the third, and situated rather nearer the micropyle. They 
are known as co-operating cells. The third and larger cell, the 
ovum or egg-cell, is of greatest importance, since it gives rise to 
the embryo. 
Proofs that the Flower is a Shoot.—I. The floral receptacle is a stem 
because it bears lateral members, differing from it in shape, and developed 
acropetally, just as in an ordinary shoot. The internodes are usually 
suppressed, but this is a common occurrence in ordinary shoots. Some- 
times, too, there is a distinct internode between the pistil and other mem- 
bers, or between essential organs and perianth. It happens in some 
1 The scope of this work will not allow of reference to gymnosperms in this 
connection, 
