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THE AUSTRALIAN NATURALIST, 163 
or stamens (Wig. 4). Each bears two groups of numerous tiny 
sacs about the size of a pin’s head, called pollen sacs or micro- 
sporangia; they contain microspores or pollen grains (Fig. 4). 
Within the pollen grain or microspore is the male gametophyte, 
but reduced to but a few cells. After the germ tube of the 
pollén grain grows, and it is ready for fertilisation, there are 
within the tube two generative nuclei. These nuclei are, in most 
Cycads, motile, swimming about in the fluid of the pollen tube 
by means of a spiral band of cilia. When the pollen is car- 
ried by wind to the ovules of the female cones, it falls through 
cracks between the sporophylls and reaches the micropyle of the 
ovule. A drop of sticky fluid at the apex of. the micropyle 
catches the grain, and on shrinking draws it down to the 
pollen chamber—a little narrow elongate cavity between the in- 
tegument and the nucellus. Here the pollen grain germinates, 
sending out the pollen tube, which sets free the motile sperma- 
tozoids. One enters an archegonium, and fertilization takes 
place by union of this cell with the oosphere of the arche- 
gonium. <A seed results. 
The Seed (Figs. 5 and 6).—The embryo consists of two elon- 
gate cotyledons (Fig. 6), plumule and radicle. This embryo is 
embedded in a mass of endosperm or food store (Fig. 6). The 
testa of the seed consists of three parts: (1) Fig. 5. (a) Outer 
skin, of bright red or yellow colour. (2) (b) Inner soft pulp 
of cream colour. (3) (c) Hard woody “nut” immediately sur- 
rounding and protecting the embryo. / 
The function of the pulpy mass and bright, outer testa would 
seem to be either :— 
(1) To attract animals to eat the pulp and carry away the 
seeds, or (2) the pulp forms a soft mass of natural manure to 
give a start to the germinating embryo. 
Germination—On germination, the radicle grows rapidly 
through a weak place at the base of the hard nut, and pushes 
deeply down into the soil, a young root being usually six inches 
long before the plumule appears.. 
The root is thick and fleshy, and seems to absorb a large 
quantity of the food supply stored in the endosperm of the seed. 
This is absorbed by the upper part of the cotyledons, which 
remain within the endosperm and send the food on to the grow- 
ing plant (Fig 6). Later the first leaf appears, and for some 
time the cotyledons are still absorbing ‘the food store within the 
nut. 
