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 exigua Nutt.) Leafy branch, bearing two 

 pistillate catkins. 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." Though a perianth 

 is wanting pollination is accomplished by insects. 



