STAMENS AND PISTIL 129 
The stamens, which form the next ring (sometimes 
a double ring or a close spiral), are much less leaf- 
like than the sepals or petals, yet there can be no 
doubt that they are descended from leaf-shaped 
organs; this is especially clear from the study of cer- 
tain primitive fossil types, in which the corresponding 
organs which bear the pollen are actually leaf-like. 
In most of the present-day Seed Plants the stamens 
conform to a uniform type—a slender stalk (filament) 
bearing a head (anther) containing four chambers, in 
which are produced pollen grains, which escape when 
the flower is mature by the splitting of the enclosing 
walls. The ways in which the pollen is then conveyed 
to the pistil of other flowers have been referred to 
briefly on a previous page (p. 82). The stamens in 
many flowers are few, and their number usually 
bears a relation to the number of the other 
floral parts; in other flowers, for instance Rose and 
St. John’s wort (Hypericum), they are of large and 
indefinite number. The peculiar arrangement of the 
pollen in Orchids has been already noted (p. 94). 
The final ring of modified leaves in our typical 
flower constitutes the pistil, formed of one or many 
carpels, the essential structure of which has been 
touched on already (p. 82). In the present place it 
is desired only to point out some of the leading modi- 
fications which the pistil undergoes, so that its struc- 
ture as seen by the naked eye may be understood. In 
the simpler forms of carpel, the affinity to leaves is 
still evident, though in forms of pistil made up of a 
number of carpels this may be very difficult to trace. 
With the Pea, for instance, we may begin, as present- 
ing a very simple example. Take an oblong leaf like 
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