BIRCH FAMILY 
knife that it has become the favorite tree for arbor-walks in 
parks. 
The flowers are moneecious ; the staminate flowers appear 
in long, loose, pendulous catkins from axillary buds. The pis- 
tillate, in loose half-erect catkins at the end of the spray. 
Each pistillate flower is subtended by a bract which expands 
with the growth of the fruit into a sort of leaf which gathers 
around and protects asmall oval nut. These fruit clusters 
often remain on the trees long after the leaves have fallen, 
The tree can be easily raised from the seed which does not 
germinate until the second year. Traces of Carpinus have 
been found in the tertiary rocks of Alaska and in the upper 
miocene of Colorado and Nevada, regions from which the 
genus has entirely disappeared. 
