FOR ARTIFICIAL REPRODUCTION. 549 



climate, and the comparative density of the standing;- crop 

 influence matters, so that sterile periods are shortened by mild 

 climate ; in extensive dense mountain-forests they are usually 

 more prolonged than in isolated woods more easily aftected by 

 changes in the weather. The species which usually fructify 

 only periodically are : beech, Scotch pine, oak, sweet chestnut 

 and larch ; on the other hand, in fairly mild climates, hornbeam, 

 sycamore and other maples, lime, silver-fir, ash, elms, black 

 alder, birch, &c. fructify almost every year. 



The beech produces fruit after the longest intervals and with 

 the most marked periodicity. In Germany, an abundant beech 

 seed-year can be expected only every 10 years, sometimes as 

 many as 10 — 15 years pass without any seed at all. 



[In France and Britain, beech seed-years occur more frequently 

 (every 5 or 6 years), except in the Vosges, Jura and Alps, (every 

 10 to 15 years), but according to Mathieu,* partial seed-years are more 

 frequent in mountainous regions than in lowlands and hills. — Tr.] 



In mountains up to moderate altitudes, there is (in Germany) 

 a small production of beech-mast every 3 or 4 years which is 

 not without value for natural reproduction. Two successive 

 abundant beech-mast years are rare events, and then a longer 

 period lapses before another seed-year occurs. 



The Scotch pine, spruce, Cembran pine, oaks and sweet 

 chestnut fructify at intervals of 3 — 5 years. Most of these 

 species produce some fruit every year in lowlands, especially 

 oaks and Scotch pine, provided the weather is at all favourable, 

 but complete crops of seed occur only as stated. Oaks and 

 chestnut trees produce most fruit in years of good vintage. 

 The seed-crops of both spruce and Scotch pine are generally 

 abundant ; the fertility of the spruce, however, gi-eatly depends 

 on the altitude at which it is growing, and the consequent 

 climate of its locality. At altitudes over 1,000 meters (3,280 

 feet) spruce seed-years occur only every 8 — 10 years. The 

 above-mentioned trees do not, however, possess the same 

 marked periodicity in seed-bearing as the beech. 



Under favourable circumstances, hornbeam, birch, sycamore 



* Flore Forcstitrc ; Berger Levrault et Cie., Nancy, 1877. 



