153 
On the Species of the Genus Primula in Essex. 
nor in the size, shape, or colour of the calyx or corolla, 
except that the tube of the latter accommodates itself slightly 
to suit the difference in the position of the anthers. It is 
probable that the two forms never appear on the same plant 
(although this is stated to have occurred in one locality), 
and the plants invariably bear, year after year, flowers of the 
same form. Although there are two forms of flowers, each 
form is hermaphrodite— i. e., it possesses both male and 
female organs. 
The heterostylism of the Cowslip was first noticed by 
Perzoon in 1794, 8 but for many years it was disregarded as 
an accidental phenomenon, until Mr. Darwin came with his 
keen observation and untiring energy to enquire into the 
matter. He showed in a paper read before the Linnean 
Society, 9 and more fully in his ‘Forms of Flowers’ (1877), 
that heterostylism is one of the most curious and interesting 
of all the many contrivances _by which cross-fertilization is 
ensured in the vegetable kingdom. His first idea was that 
Primulas were on then* way to become dioecious—that the 
long-styled flower with its prominent stigma was the most 
feminine form, and the short-styled flower with its prominent 
anthers was the most masculine form ; but the discovery that 
the short-styled flowers were actually the most fertile upset 
this idea. On making experiments he found that the two 
forms require a reciprocal union to ensure full fertility; or in 
other words, that a flower, say of the long-styled form, is 
very largely sterile when fertilized with pollen from another 
flower of the same form (a union which he calls “illegiti¬ 
mate”), but produces its full complement of healthy seeds 
when fertilized with pollen from a short-styled blossom 
(“legitimate” union) and vice versa. Darwin shows that if a 
bee visits a short-styled primrose flower it dusts its proboscis 
with pollen near the base. If then it goes to flowers of the 
same plant, or flowers on another plant of the same form, no 
pollen is deposited on the stigmas: on the contrary, more 
will, in all probability, attach itself to the insect’s proboscis ; 
but if the bee visits some flowers on a plant of the opposite 
form, pollen is (as required) placed at once on the stigma, 
because that part of the bee’s proboscis which touches the 
anthers in one case touches the stigma in the other, and thus 
is reciprocal cross-fertilization effected. Were the anthers 
and stigma placed on the same level, the flowers would more 
likely than not be self-fertilized; and this Darwin has shown 
8 £ Forms of Flowers,’ p. 14. 
9 Proc. Linn. Soc. (Bot.), vol. vi. (1862), p. 77, and vol. x. (1869), 
p. 398 
M 
