SPRUCE AND BALSAM FIR TREES. 19 



The male and female flowers of the firs are produced on different 

 branches of the same tree. Each sort is borne on branchlets of the 

 previous year's growth, the male flowers on the lower-crown branches 

 and the female flowers on the topmost branches of the same tree. 

 Male flowers, which bear pollen, are elongated, cylindrical, scaly 

 bodies hanging singly among the leaves from the lower side of 

 branches. The female flowers, which produce cones and seeds, are 

 short, spherical, rounded or elongated, scaly bodies standing erect 

 and singly on branches of the uppermost part of the crown. The 

 cones, whose erect or nearly erect position is unique and distinctive 

 of all firs, mature in one season. (Pis. IX, XI, and XII, b.) 

 During autumn their thin, closely packed, overlapping scales grad- 

 ually become loosened from the central spikelike axis (PL IX, c, 

 and PI. XXIII) and fall away with their winged seeds, two of 

 which are borne under each scale (PI. XIV, 5, and PI. XVII, 

 b) ; no fertile or perfect seeds are borne under scales at the two 

 ends of the cones. The spikelike woody axes of the cones remain 

 attached to their branches for several years. (Pis. IX, c, and PI. 

 XII, 5.) Morphologically these woody axes are modified twigs. The 

 breaking up of mature cones on the trees is characteristic of no other 

 group of our cone bearers, except the deciduous-leafed Taxodium 

 ("cypress") of south Atlantic forests. As the ripe cones of firs 

 break up strong winds may blow the seeds several hundred feet 

 from the parent trees, but as a rule the seeds fall near the mother 

 tree or are wafted not more than 50 or 100 feet away. The seeds 

 have peculiar resin cells, which may be seen by cutting into the seed 

 coat. Under ordinary conditions the vitality of fir seeds rarely, if 

 ever, endures longer than a single season, and as a rule the per- 

 centage of germination is comparatively low (50 per cent or less). 

 Seed-leaves (cotyledons, the first foliar organs to appear when the 

 seed germinates) range from 4 to 10 in number and are flat. (PI. 

 XXIII, c.) 



Fir trees are of great commercial importance on account of the 

 excellent saw timber the larger species produce, while some of them 

 are important also because they form protection forests on steep 

 slopes at high elevations where few other conifers can live. They are 

 moderately long-lived trees, their age limit ranging from about 200 

 to 350 years; much is yet to be learned, however, concerning. their 

 longevity. 



Eleven species of firs inhabit the United States. Six of them occur 

 within the Rocky Mountain region (of the United States and Can- 

 ada) , while four are common to both the Rocky Mountain and Pacific 

 slope regions. One species ranges from the Canadian Rocky Moun- 

 tain region eastward to the Atlantic coast, where it is common both in 

 our northeastern States and in adjacent parts of Canada. One of 



