244 PLANT LIFE 
plant does the same, but the subsidiary 
events that have happened during its evolu- 
tion obscure its record. However, we find 
two kinds of sporangia, one commonly 
grouped in a cluster of two or four, and form- 
ing the so-called pollen sacs borne on each 
of the stamens. The pollen sacs produce the 
spores or pollen grains in much the same 
way as the spores are formed in a fern. But 
the other sort of sporangium is less easily 
recognised (Fig. 28). It is often known as an 
ovule, and the ovules are situated inside a 
closed cavity called the ovary, which forms 
the lower part of the pistil of the flower. 
Each ovule (or sporangium) usually contains 
but one spore, and this is not, like the pollen 
grain, thrown out of the sporangium, but 
germinates inside it, and produces an egg as 
well as a number of other cells. Moreover, 
the sporangium is retained within the ovary, 
and hence the methods of fertilisation which 
are appropriate for a fern would clearly be 
impossible here. As a matter of fact, the 
pollen grain, 7. e. the spore from which the 
male gamete will be derived, has to be brought 
into special relation with that part of the 
flower in which the ovule is situated. At the 
summit of the ovary there is a specialised 
structure called the stigma. This is often 
viscid just when the ovules are mature, and 
thus any pollen which falls on to the stigma 
is retained. 
The pollen grain or spore already contains 
