78 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 1, NO. 2. 
or even later. In the early spring of 1898, Salix discolor l^egan its 
blooming period on April 12th, seventeen days later than TriUinm 
nivalc and exactly two weeks later than Erigcnia bulhosa. The 
spring of 1899 was preceded by a prolonged period of unusually 
cold \veather in the month of February, and accordingly our first 
vernal flowers were slow in making their appearance. Ikit after 
the opening of the flowers of Trillium nivalc on April nth, and 
those of Erigcnia bulhosa on the following day, April 12th, the 
season progressed very rapidly and brought out the first flowers 
of Salix discolor on April 17th, only five days later than Erigcni.i 
bulhosa. 
The appearance of the first willow catkins, covered with blos- 
soms, is an event of no small importance to the anthophilous in- 
sects, whose time of flight corresponds with the l)looming period 
of our willows. One of the most important features of the willow- 
blossoms is the presence of catkins bearing only male or staminate 
flowers on one plant, and catkins with only female or pistillate 
flowers on a different plant. This distribution of the two sexes 
on two different plants is called dioecism, and is a contrivance by 
which cross-fertilization is made a necessity. 
The willow family (Salicaceae) comprises the species, be- 
longing either to the genus Salix (the willows) or to the genus 
Populus (the poplars, aspens), and the members of this family 
are without exception dioecious. The species of Populus are 
anemophilous. They depend on the currents of air to transport 
their pollen from the male flowers to the stigmas of the female 
flowers. Their flowers are neither fragrant, nor do they secrete 
nectar. They possess practically nothing attractive to insects, ex- 
cept, perhaps, the dry, smooth-coated pollen of the male flowers, 
which is not appreciated by insect Ansitors. The latter may be 
observed in exceptional cases on the male flowers of poplars, feed- 
ing on pollen, but their visits are of no advantage to the flowers, 
as the same insects never pay any attention to the female flowers. 
The other members of the family, the species of Salix (the 
willows), have adopted entirely different methods to insure cross- 
fertilization. They rely for this purpose on the aid of insects. 
They are decidedly entomophilous. Owing to the abundant pro- 
duction of nectar and the fragrance of their flowers, they secure 
an ample set of visitors, and in addition to this their male flowers 
offer a full supply of damp, adherent pollen, which is a further 
source of attraction to pollen-collecting and pollen-eating insects. 
The flowers of our earliest willow, Salix discolor, Muhl., are well 
provided in this respect, and attract numerous visitors, belonging 
to widely separated orders of insects. These flowers are of a very 
