THE THREE FORMS OF LYTIIRUM SALICARIA. 195 
fact is in itself curious, and shows by what insensibly graduated 
steps nature moves. If this tendency were carricd out the 
mid-styled form would become a female, depending for its fer- 
tilization on two sets of stamens in the long- and short-styled 
forms; and these two forms would reciprocally fertilize each other 
like the two forms of Primula or Linum; but there would be no 
approach to a diecious condition. 
As the case of the trimorphic species of Zythrum is so com- 
plicated, and as it is easier to perceive the relations of the sexes 
in the animal than in the vegetable kingdom, it may be worth 
while to give, before concluding, a somewhat elaborate simile. 
We may take the case of a species of Ant, and suppose all the 
individuals invariably to live in three kinds of communities ; in 
. the first, a large-sized female (not to specify other differences) 
living with six middle-sized and six small-sized males; in the 
second, a middle-sized female with six large- and six small-sized 
males; and in the third community, a small-sized female with six 
large- and six middle-sized males. Each one of these three 
females, though enabled to unite with any male, would be nearly 
sterile with her own two sets of males, and likewise with two 
other sets of males living in the other two communities; for she 
would be fully fertile only when paired with a male of her own 
size. Hence the thirty-six males, distributed by half-dozens in 
the three communities, would be divided into three sets of a 
dozen each; and these sets, as well as the three females, would 
differ from each other sexually in exactly the same manner as 
distinct species of the same genus. Moreover the two sets of 
males living in the community of the extraordinarily fertile 
middle-sized female would be less potent sexually than the males 
of corresponding size in the two other communities. Lastly, we 
should find that from the eggs laid by each of the three females, 
all three sorts of females and all three sorts of males were 
habitually reared—proving to demonstration that all belonged to 
one and the same species. 
To appreciate fully this remarkable case of the reciprocally tri- 
morphic species of Lythrum, we may take a glance at the two great 
kingdoms of nature and search for anything analogous. With 
animals we have the most astonishing diversity of structure in 
the so-called cases of alternate generation, but as such animals 
have not arrived at maturity, they are not properly comparable 
with the forms of Zythrum. With mature animals we have 
extreme differences in structure in the two sexes; we have in 
