458 STRUCTURE AND LIFE HISTORIES 
to its failure to develop sufficient mechanical tissue (wood) 
in its smaller branches to hold them erect. 
All willows are dioecious. The imperfect, apetalous 
flowers occur crowded together on scaly spikes called 
catkins (Fig. 340). Each scale bears one flower in its axil. 
The staminate flowers consist usually of two (sometimes 
FIG. 341. Willow (Salix). Leafy branch, bearing two pistillate cat- 
kins. Staminate flower above, at the left; pistillate flower below, at the 
right. (After Britton and Brown.) 
three to ten) stamens (Fig. 341). In some species the 
stamens are united. When the flower buds open, early 
in spring, the numerous hairs on the scales or filaments 
(one or both) give the soft, fur-like appearance, which 
suggested the name "pussy-willow." As in the pines, 
pollination is accomplished by the wind. 
