PLANT ORGANS AND ORGANISMS 
157 
development may occur. Thus, in Viola, the end of the style is a 
swollen knob on the under surface of which is a concave stigma with 
a flap or peg. In the genus Canna the style is an elongate blade-like 
flattened body with a sub-terminal stigma. In forms of the Cam- 
panulacecE the style is closely covered with so-called collecting hairs. 
On these the anthers deposit their pollen at an early period before 
the flowers have opened. Later, when the flowers open, insects 
remove the pollen after which the collecting hairs wither. The stig- 
mas then curl apart to expose their viscid stigmatic hairs. In this 
instance there are two distinct and at separate times functioning hairs 
on the stylar prolongation, viz.: (a) collecting stylar hairs, functioning 
for pollen collection and distribution; and ( b ) stigmatic hairs for pol- 
len reception from another flower. In Vinca the style swells near its 
extremity into a broad circular stigma and then is prolonged into a 
short column bearing a tuft of hairs that prevents the entrance of 
insect thieves into the flower. In the genus Iris the common style 
breaks up at the insertion of the perianth into three wide petaloid 
style arms. Each of these bifurcates at its extremity. On the 
lower or outer face of this is a transverse flap that bears the stigmatic 
papillae. In Physostigma the style enlarges at its extremity into a 
flap-like swelling which bears a narrow stigmatic surface. Finally 
in Sarracenia the single style of the five-carpelled pistil enlarges 
above into a huge umbrella-like portion with five radiating ribs. At 
the extremity of each bifid end of each rib is a minute peg-like stig- 
matic surface. 
The Stigma. — This is usually a viscid papillose surface of greater or 
less expanse functioning for pollen reception. In wind-pollinated 
flowers such as the grasses, the stigmas are the numerous feathery 
hairs which cover the ends of the styles and intended to catch flying 
pollen grains. In animal-pollinated flowers, the stigmas are usually 
small restricted knobs, lines or depressions. The stigmatic papillae 
vary in size in different plants and even may vary on different 
individuals of the same species. Thus in the long styles of Primula, 
the stigmatic papillae are elongated columnar hair-like structures, 
whereas in the short styles of short-styled flowers the papillae are 
small knob-like cellular swellings. 
