670 UTILIZATION OF THE FRUITS OF FOREST TREES. 



starch has accumulated, another seed-year occurs. This 

 apparently explains a number of phenomena in seedbearing. 

 Thus the period of rest is shorter, the more favourable are 

 the conditions of illumination for a tree ; the more the crown 

 is crowded and shaded, the longer is seedbearing delayed. 



Increased exposure to heat expedites fructification ; nume- 

 rous prolonged observations in Prussia have proved this well- 

 known law ; Bernhardt, Weise, Hellwig, v. Alten and 

 Schwappach* have shown this to be true. 



Thus, in the warm Ehine provinces, there are good crops of 

 acorns every two years, while in E. Prussia, only every six 

 years. But for Scots pine, in Brandenburg every two years 

 there is a good crop of seed, while in Khenish Prussia and 

 Silesia, only every ten years, so that the law is not true 

 always, for age, soil, condition of crops, etc., must be con- 

 sidered as well as the effects of heat. 



The following figures are generally true as 'regards the 

 recurrence of seed-years for the same individual tree : 



Recurrence of seed-years. 



Species. 



Willow, poplar, birch, alder, cypress, elm, common 



pine, larch. 

 Hornbeam, ash, maple, lime, spruce, 



Silver-fir, Cembran pine, sweet-chestnut. 



Every 2 years ... 

 ., 2 to 4 years 

 4 to 6 



6 to 10 



Oak, beech. 



According to this statement the lightest seeds are produced 

 the most frequently, and this is a support of the truth of 

 Har tig's theory. But it must be proved also how much 

 reserve material is taken from the wood by a mast, and how 

 much seed-albumen is formed in the particular seed-year. 

 The weather during the seed-year decides also whether or not 

 fruit is formed from the flower. 



Acorn years are distinguished by great heat and drought 

 (vintage-years) ; should two successive, dry, hot years occur, 



* Schwappach, "Die SaimMiproiluciioM <ler wiclit listen \Vnl<llu>l/;irt<>ii in 

 I'l'cusscii.' 1 /(Mtseh.f. F. u .l;i;_M\vrsrn. 1S'J5. Airxt(nn : ut 20 yours' observations. 



